Update:

I'm unable to edit my original question (403 Forbidden Error), so here is the relevant code from our custom modules.

Complex Module

openerp.py

...
    'depends': ['base', 'account', 'account_accountant', 'sale', 'sale_order_travis'],
    'installable': True,
    'auto_install': False,
    'application': True,
...

sale_discount.py

from __future__ import division
from openerp import fields, models, api, osv
import openerp.addons.decimal_precision as dp
import math
class saleorder_discount(models.Model):
    _inherit = 'sale.order'
    fee_type = fields.Selection([('Blind Ship', 'Blind Ship'), ('Blind Ship Rush', 'Blind Ship Rush')], string='Fee Type',
                                     states={'draft': [('readonly', False)]},
                                     help='Fee is percentage of subtotal plus fixed fee')
    minimum_order_fee_exempt = fields.Boolean('Exempt from Minimum Order Fee', help='If checked, customer will not be charged any fees even if the order is under the minimum.')
    discounted_amount = fields.Float(string='Fees', store=True, readonly=True, compute='compute_amounts')
    amount_total = fields.Float(string='Total', digits=dp.get_precision('Account'),
                                store=True, readonly=True, compute='compute_amounts')
    def _prepare_invoice(self, cr, uid, order, lines, context=None):
        res = super(saleorder_discount, self)._prepare_invoice(cr, uid, order, lines, context=context)
        res.update({'fee_type' : order.fee_type,
                    'minimum_order_fee_exempt' : order.minimum_order_fee_exempt})
        return res
    @api.one
    @api.onchange('minimum_order_fee_exempt','fee_type')
    @api.depends('order_line.price_subtotal', 'discounted_amount', 'fee_type', 'minimum_order_fee_exempt')
    def compute_amounts(self):
        self.amount_untaxed = sum(line.price_subtotal for line in self.order_line)
        # Get "order amount" without shipping charges because they don't count towards the minimum
        price_shipping = 0
        for line in self.order_line:
            if line.product_id.default_code in ['mage_shipping','Shipping Charge'] or line.name in ['Magento Shipping','Shipping Charge']:
                price_shipping += line.price_subtotal
            elif line.name in ['Discount - Low Order Fee']:
                self.minimum_order_fee_exempt = True
        price_subtotal_excluding_shipping = self.amount_untaxed - price_shipping
        val = 0
        minimum_order_amt = 25.00
        if self.name.count('-') >= 2:
            self.minimum_order_fee_exempt = True
        if price_subtotal_excluding_shipping < minimum_order_amt and not self.minimum_order_fee_exempt:
            low_order_fee = 10.00
        else:
            low_order_fee = 0.00
        for line in self.order_line:
            val += self._amount_line_tax(line)
        print "Fee Type: " + str(self.fee_type)
        if self.fee_type == 'Blind Ship Rush':
            fee_fixed = 20.00
            fee_percentage = 0.05
            amount_to_dis = round( (price_subtotal_excluding_shipping) * (fee_percentage) , 2)
            self.discounted_amount = amount_to_dis + fee_fixed + low_order_fee
            self.amount_total = self.amount_untaxed + val + amount_to_dis + fee_fixed + low_order_fee
        elif self.fee_type == 'Blind Ship':
            fee_fixed = 10.00
            fee_percentage = 0.035
            amount_to_dis = round( (price_subtotal_excluding_shipping) * (fee_percentage) , 2)
            self.discounted_amount = amount_to_dis + fee_fixed + low_order_fee
            self.amount_total = self.amount_untaxed + val + amount_to_dis + fee_fixed  + low_order_fee
        elif price_subtotal_excluding_shipping < minimum_order_amt and not self.minimum_order_fee_exempt:
            self.discounted_amount = low_order_fee
            self.amount_total = self.amount_untaxed + val + low_order_fee
        else:
            self.discounted_amount = 0
            self.amount_total = self.amount_untaxed + val
        print "Fees: $" + str(self.discounted_amount)
        print "Amount Total: $" + str(self.amount_total)

Simple Module

It is changing position of a field on the product view. Completely unrelated from sales order.

...
    <record id="product_mpn_search_view" model="ir.ui.view">
        <field name="name">Search for MPN (Supplier Default Code)</field>
        <field name="model">product.template</field>
        <field name="inherit_id" ref="product.product_template_search_view"/>
        <field name="arch" type="xml">
            <field name="name" position="after">
                <field name="seller_ids" string="MPN" filter_domain="[('seller_ids.product_code','ilike',self)]" />
            </field>
        </field>
    </record>
...