Destination Charges

shipment_decorator.rb

Spree::Shipment.class_eval do
  after_save :ensure_destination_charge

  def ensure_correct_adjustment
    if order.destination_charges[0]
      # recalculate
    else
      order.destination_charges << create a new one
    end
  end
end

Spree::Order.class_eval do
  has_many :destination_charges

end