diff --git a/app/controllers/spree/admin/products_controller_decorator.rb b/app/controllers/spree/admin/products_controller_decorator.rb
deleted file mode 100644
index 01058e6..0000000
--- a/app/controllers/spree/admin/products_controller_decorator.rb
+++ /dev/null
@@ -1,26 +0,0 @@
-module Spree
-  module Admin
-    ProductsController.class_eval do
-      def variant_prices
-        id = session[:current_price_book_id]
-        session.delete(:current_price_book_id)
-
-        @current_price_book = id.present? ? PriceBook.find(id) : PriceBook.default
-        
-        # need every variant/price(for the current price book) pair
-        # I had to do this ridiculous sort to get the master first since the scope orders by position,
-        # but for some reason the position is screwed up for master (it's not first)
-        @variants = @product.variants_including_master.partition {|v| v.is_master?}.flatten
-        
-        @prices = {}
-        
-        @variants.each do |variant|
-          @prices[variant.id] = variant.prices.detect {|price| price.price_book_id == @current_price_book.id} # possibly nil
-        end
-        
-        @price_books    = PriceBook.order('priority')
-        @default_price_book  = @price_books.detect {|pb| pb.default?}
-      end
-    end
-  end
-end
diff --git a/app/controllers/spree/admin/spree_price_books/products_controller_decorator.rb b/app/controllers/spree/admin/spree_price_books/products_controller_decorator.rb
new file mode 100644
index 0000000..c24c570
--- /dev/null
+++ b/app/controllers/spree/admin/spree_price_books/products_controller_decorator.rb
@@ -0,0 +1,30 @@
+module Spree
+  module Admin
+    module SpreePriceBooks
+      module ProductsControllerDecorator
+        def variant_prices
+          id = session[:current_price_book_id]
+          session.delete(:current_price_book_id)
+
+          @current_price_book = id.present? ? PriceBook.find(id) : PriceBook.default
+
+          # need every variant/price(for the current price book) pair
+          # I had to do this ridiculous sort to get the master first since the scope orders by position,
+          # but for some reason the position is screwed up for master (it's not first)
+          @variants = @product.variants_including_master.partition {|v| v.is_master?}.flatten
+
+          @prices = {}
+
+          @variants.each do |variant|
+            @prices[variant.id] = variant.prices.detect {|price| price.price_book_id == @current_price_book.id} # possibly nil
+          end
+
+          @price_books    = PriceBook.order('priority')
+          @default_price_book  = @price_books.detect {|pb| pb.default?}
+        end
+      end
+    end
+  end
+end
+
+Spree::Admin::ProductsController.prepend Spree::Admin::SpreePriceBooks::ProductsControllerDecorator
diff --git a/app/helpers/spree/base_helper_decorator.rb b/app/helpers/spree/base_helper_decorator.rb
deleted file mode 100644
index cf63ad4..0000000
--- a/app/helpers/spree/base_helper_decorator.rb
+++ /dev/null
@@ -1,7 +0,0 @@
-module Spree
-  BaseHelper.class_eval do
-    def display_price(product_or_variant)
-      product_or_variant.price_in(current_currency, current_store.id, spree_current_user.try(:price_book_role_ids)).display_price.to_html
-    end
-  end
-end
diff --git a/app/helpers/spree/spree_price_books/base_helper_decorator.rb b/app/helpers/spree/spree_price_books/base_helper_decorator.rb
new file mode 100644
index 0000000..55b2263
--- /dev/null
+++ b/app/helpers/spree/spree_price_books/base_helper_decorator.rb
@@ -0,0 +1,11 @@
+module Spree
+  module SpreePriceBooks
+    module BaseHelperDecorator
+      def display_price(product_or_variant)
+        product_or_variant.price_in(current_currency, current_store.id, spree_current_user.try(:price_book_role_ids)).display_price.to_html
+      end
+    end
+  end
+end
+
+Spree::BaseHelper.prepend Spree::SpreePriceBooks::BaseHelperDecorator
diff --git a/app/models/spree/order/currency_updater_decorator.rb b/app/models/spree/order/currency_updater_decorator.rb
deleted file mode 100644
index 185eacd..0000000
--- a/app/models/spree/order/currency_updater_decorator.rb
+++ /dev/null
@@ -1,33 +0,0 @@
-module Spree
-  class Order < Spree::Base
-    CurrencyUpdater.class_eval do
-
-      # Returns the price object from given item
-      def list_price_from_line_item(line_item)
-        line_item.variant.list_price_in(currency, store_id, user.try(:price_book_role_ids))
-      end
-
-      # Returns the price object from given item
-      def price_from_line_item(line_item)
-        line_item.variant.price_in(currency, store_id, user.try(:price_book_role_ids))
-      end
-
-      # Updates price from given line item
-      def update_line_item_price!(line_item)
-        list_price = list_price_from_line_item(line_item)
-        price = price_from_line_item(line_item)
-
-        if price
-          line_item.update_attributes!(
-            currency: price.currency,
-            list_price: list_price.price,
-            price: price.price
-          )
-        else
-          raise RuntimeError, "no #{currency} price found for #{line_item.product.name} (#{line_item.variant.sku})"
-        end
-      end
-
-    end
-  end
-end
diff --git a/app/models/spree/order/spree_price_books/currency_updater_decorator.rb b/app/models/spree/order/spree_price_books/currency_updater_decorator.rb
new file mode 100644
index 0000000..f23aa52
--- /dev/null
+++ b/app/models/spree/order/spree_price_books/currency_updater_decorator.rb
@@ -0,0 +1,35 @@
+module Spree
+  class Order
+    module SpreePriceBooks
+      module CurrencyUpdaterDecorator
+        # Returns the price object from given item
+        def list_price_from_line_item(line_item)
+          line_item.variant.list_price_in(currency, store_id, user.try(:price_book_role_ids))
+        end
+
+        # Returns the price object from given item
+        def price_from_line_item(line_item)
+          line_item.variant.price_in(currency, store_id, user.try(:price_book_role_ids))
+        end
+
+        # Updates price from given line item
+        def update_line_item_price!(line_item)
+          list_price = list_price_from_line_item(line_item)
+          price = price_from_line_item(line_item)
+
+          if price
+            line_item.update_attributes!(
+              currency: price.currency,
+              list_price: list_price.price,
+              price: price.price
+            )
+          else
+            raise RuntimeError, "no #{currency} price found for #{line_item.product.name} (#{line_item.variant.sku})"
+          end
+        end
+      end
+    end
+  end
+end
+
+Spree::Order::CurrencyUpdater.prepend Spree::Order::SpreePriceBooks::CurrencyUpdaterDecorator
diff --git a/app/models/spree/price_decorator.rb b/app/models/spree/price_decorator.rb
deleted file mode 100644
index a02defe..0000000
--- a/app/models/spree/price_decorator.rb
+++ /dev/null
@@ -1,53 +0,0 @@
-Spree::Price.class_eval do
-
-  belongs_to :price_book
-
-  has_many :store_price_books, through: :price_book
-
-  validate :ensure_proper_currency
-  validates :price_book_id, presence: true
-
-  before_validation :ensure_price_book
-
-  after_create :populate_children
-  after_update :update_children
-
-  delegate :product, to: :variant
-
-  scope :by_currency, -> (currency_iso) { where(currency: currency_iso) }
-  scope :by_role, -> (role_ids) { prioritized.where(spree_price_books: { role_id: role_ids }) }
-  scope :by_store, -> (store_id) { joins(:store_price_books).where(spree_store_price_books: { store_id: store_id }) }
-  scope :list, -> { prioritized.where(spree_price_books: { discount: false }) }
-  scope :prioritized, -> { includes(:price_book).order('spree_price_books.priority DESC, spree_prices.amount ASC') }
-
-  private
-
-  def ensure_price_book
-    self.price_book ||= Spree::PriceBook.default
-  end
-
-  def ensure_proper_currency
-    unless currency == price_book.currency
-      errors.add(:currency, :match_price_book)
-    end
-  end
-
-  def populate_children
-    price_book.children.each do |book|
-      if price = book.prices.find_by_variant_id(self.variant_id)
-        price.update_attribute :amount, self.amount * book.price_adjustment_factor
-      else
-        book.prices.create amount: (self.amount * book.price_adjustment_factor), currency: book.currency, variant_id: self.variant_id
-      end
-    end
-  end
-
-  def update_children
-    price_book.children.each do |book|
-      if price = book.prices.find_by_variant_id(self.variant_id)
-        price.update_attribute :amount, self.amount * book.price_adjustment_factor
-      end
-    end
-  end
-
-end
diff --git a/app/models/spree/role_decorator.rb b/app/models/spree/role_decorator.rb
deleted file mode 100644
index 60e4f1b..0000000
--- a/app/models/spree/role_decorator.rb
+++ /dev/null
@@ -1,6 +0,0 @@
-module Spree
-  Role.class_eval do
-    has_many :price_books
-    scope :with_price_book, -> { where(id: Spree::PriceBook.pluck(:role_id).uniq) }
-  end
-end
diff --git a/app/models/spree/spree_price_books/price_decorator.rb b/app/models/spree/spree_price_books/price_decorator.rb
new file mode 100644
index 0000000..47883b1
--- /dev/null
+++ b/app/models/spree/spree_price_books/price_decorator.rb
@@ -0,0 +1,55 @@
+module Spree::SpreePriceBooks::PriceDecorator
+  def self.prepended(base)
+    base.belongs_to :price_book
+
+    base.has_many :store_price_books, through: :price_book
+
+    base.validate :ensure_proper_currency
+    base.validates :price_book_id, presence: true
+
+    base.before_validation :ensure_price_book
+
+    base.after_create :populate_children
+    base.after_update :update_children
+
+    base.delegate :product, to: :variant
+
+    base.scope :by_currency, -> (currency_iso) { where(currency: currency_iso) }
+    base.scope :by_role, -> (role_ids) { prioritized.where(spree_price_books: { role_id: role_ids }) }
+    base.scope :by_store, -> (store_id) { joins(:store_price_books).where(spree_store_price_books: { store_id: store_id }) }
+    base.scope :list, -> { prioritized.where(spree_price_books: { discount: false }) }
+    base.scope :prioritized, -> { includes(:price_book).order('spree_price_books.priority DESC, spree_prices.amount ASC') }
+  end
+
+  private
+
+  def ensure_price_book
+    self.price_book ||= Spree::PriceBook.default
+  end
+
+  def ensure_proper_currency
+    unless currency == price_book.currency
+      errors.add(:currency, :match_price_book)
+    end
+  end
+
+  def populate_children
+    price_book.children.each do |book|
+      if price = book.prices.find_by_variant_id(self.variant_id)
+        price.update_attribute :amount, self.amount * book.price_adjustment_factor
+      else
+        book.prices.create amount: (self.amount * book.price_adjustment_factor), currency: book.currency, variant_id: self.variant_id
+      end
+    end
+  end
+
+  def update_children
+    price_book.children.each do |book|
+      if price = book.prices.find_by_variant_id(self.variant_id)
+        price.update_attribute :amount, self.amount * book.price_adjustment_factor
+      end
+    end
+  end
+end
+
+Spree::Price.prepend Spree::SpreePriceBooks::PriceDecorator
diff --git a/app/models/spree/product_decorator.rb b/app/models/spree/spree_price_books/product_decorator.rb
similarity index 61%
rename from app/models/spree/product_decorator.rb
rename to app/models/spree/spree_price_books/product_decorator.rb
index 4fc681e..0708f24 100644
--- a/app/models/spree/product_decorator.rb
+++ b/app/models/spree/spree_price_books/product_decorator.rb
@@ -1,6 +1,7 @@
-Spree::Product.class_eval do
-
-  has_many :price_books, through: :master
+module Spree::SpreePriceBooks::ProductDecorator
+  def self.prepended(base)
+    base.has_many :price_books, through: :master
+  end
 
   def master_price_for(price_book)
     Spree::Price.where(
@@ -13,5 +14,6 @@ def display_master_price_for(price_book)
     price = master_price_for(price_book)
     Spree::Money.new(price.amount, currency: price_book.currency)
   end
-
 end
+
+Spree::Product.prepend Spree::SpreePriceBooks::ProductDecorator
diff --git a/app/models/spree/spree_price_books/role_decorator.rb b/app/models/spree/spree_price_books/role_decorator.rb
new file mode 100644
index 0000000..9c167fb
--- /dev/null
+++ b/app/models/spree/spree_price_books/role_decorator.rb
@@ -0,0 +1,8 @@
+module Spree::SpreePriceBooks::RoleDecorator
+  def self.prepended(base)
+    base.has_many :price_books
+    base.scope :with_price_book, -> { where(id: Spree::PriceBook.pluck(:role_id).uniq) }
+  end
+end
+
+Spree::Role.prepend Spree::SpreePriceBooks::RoleDecorator
diff --git a/app/models/spree/spree_price_books/store_decorator.rb b/app/models/spree/spree_price_books/store_decorator.rb
new file mode 100644
index 0000000..5c25812
--- /dev/null
+++ b/app/models/spree/spree_price_books/store_decorator.rb
@@ -0,0 +1,12 @@
+module Spree::SpreePriceBooks::StoreDecorator
+  def self.prepended(base)
+    base.has_many :price_books, -> {
+      select("DISTINCT (#{table_name}.id), #{table_name}.*, #{Spree::StorePriceBook.table_name}.priority").
+        order("#{Spree::StorePriceBook.table_name}.priority DESC")
+    }, through: :store_price_books
+
+    base.has_many :store_price_books
+  end
+end
+
+Spree::Store.prepend Spree::SpreePriceBooks::StoreDecorator
diff --git a/app/models/spree/user_decorator.rb b/app/models/spree/spree_price_books/user_decorator.rb
similarity index 59%
rename from app/models/spree/user_decorator.rb
rename to app/models/spree/spree_price_books/user_decorator.rb
index 0cc5885..3c9d770 100644
--- a/app/models/spree/user_decorator.rb
+++ b/app/models/spree/spree_price_books/user_decorator.rb
@@ -1,8 +1,8 @@
-Spree.user_class.class_eval do
-
+module Spree::SpreePriceBooks::UserDecorator
   # When prices are determined based on the user role we must also include nil.
   def price_book_role_ids
     [nil, spree_roles.pluck(:id)].flatten
   end
-
 end
+
+Spree::user_class.prepend Spree::SpreePriceBooks::UserDecorator
diff --git a/app/models/spree/variant_decorator.rb b/app/models/spree/spree_price_books/variant_decorator.rb
similarity index 61%
rename from app/models/spree/variant_decorator.rb
rename to app/models/spree/spree_price_books/variant_decorator.rb
index 7d5939c..319a60b 100644
--- a/app/models/spree/variant_decorator.rb
+++ b/app/models/spree/spree_price_books/variant_decorator.rb
@@ -1,22 +1,17 @@
-Spree::Variant.class_eval do
-
-  ## Associations
-
-  has_one :default_price,
-    -> { where currency: Spree::Config[:currency], price_book_id: Spree::PriceBook.default.id },
-    class_name: 'Spree::Price',
-    dependent: :destroy
-
-  has_many :prices,
-    class_name: 'Spree::Price',
-    dependent: :destroy,
-    inverse_of: :variant
-
-  has_many :price_books, -> { active.order('spree_prices.amount ASC, spree_price_books.priority DESC') }, through: :prices
-
-  ## Class Methods
-
-  ## Instance Methods
+module Spree::SpreePriceBooks::VariantDecorator
+  def self.prepended(base)
+    base.has_one :default_price,
+      -> { where currency: Spree::Config[:currency], price_book_id: Spree::PriceBook.default.id },
+      class_name: 'Spree::Price',
+      dependent: :destroy
+
+    base.has_many :prices,
+      class_name: 'Spree::Price',
+      dependent: :destroy,
+      inverse_of: :variant
+
+    base.has_many :price_books, -> { active.order('spree_prices.amount ASC, spree_price_books.priority DESC') }, through: :prices
+  end
 
   def display_list_price(currency = Spree::Config[:currency], store_id = Spree::Store.default.id, role_ids = nil)
     lp = list_price_in(currency, store_id)
@@ -39,5 +34,6 @@ def price_in(currency = Spree::Config[:currency], store_id = Spree::Store.defaul
       prices.by_currency(currency).by_role(role_ids).first
     end
   end
-
 end
+
+Spree::Variant.prepend Spree::SpreePriceBooks::VariantDecorator
diff --git a/app/models/spree/store_decorator.rb b/app/models/spree/store_decorator.rb
deleted file mode 100644
index 1e4ec91..0000000
--- a/app/models/spree/store_decorator.rb
+++ /dev/null
@@ -1,10 +0,0 @@
-Spree::Store.class_eval do
-
-  has_many :price_books, -> {
-    select("DISTINCT (#{table_name}.id), #{table_name}.*, #{Spree::StorePriceBook.table_name}.priority").
-      order("#{Spree::StorePriceBook.table_name}.priority DESC")
-  }, through: :store_price_books
-
-  has_many :store_price_books
-
-end
diff --git a/lib/spree_price_books/engine.rb b/lib/spree_price_books/engine.rb
index 1998b97..e54a74a 100644
--- a/lib/spree_price_books/engine.rb
+++ b/lib/spree_price_books/engine.rb
@@ -17,8 +17,10 @@ def self.activate
 
     config.to_prepare &method(:activate).to_proc
 
-    initializer "spree_active_shipping.register.calculators" do |app|
-      app.config.spree.calculators.shipping_methods << Spree::Calculator::Shipping::FlatMultiCurrencyRate
+    initializer "spree_price_books.register.calculators", after: "spree.register.calculators" do |app|
+      Rails.application.config.after_initialize do
+        app.config.spree.calculators.shipping_methods << Spree::Calculator::Shipping::FlatMultiCurrencyRate
+      end
     end
   end
 end