When you use a Miva shipping method I see that I can modify that at the product level (i.e. add an extra $100 to price based shipping for a particular product). Find that this could be useful but you cannot show/hide a column for those values, nor does there seem to be a way to export that value with the products. The result is that if I want to add an extra amount of $100 to some heavy steel doors (60 products) I need to drill down to the shipping tab one by one or create another special shipping method.