Thickness depending letter or package shipping mod

Shipping is very expensive, especially if you are selling cheap products like used books or clothes. These cost are most of the time more expensive then the products it selves.

I wrote this shipping module to automatically let the shop determine if a product, or a couple of products can be sent by letter mail, and calculate the shipping costs. If this is not possible, package mail cost are being calculated.

This shipping module creates an extra field in admin >categories>products product information, right under weight field. Thickness of a product can be filled in, in this field. If a product can never be shipped by letter mail, just fill in a thickness that is higher then the allowed maximum thickness for letter mail.

Maximum thickness for letter mail, added weight and thickness in case of letter mail can be filled in, in the configuration of this module.