I've run into a little dilemma with shipping. We sell multiple products, most of which have different shipping calculations. We ship some flat rate (but in different flat rate boxes, so setting up a standard flat rate won't work), we also ship international flat rate, we also ship some products as $x for the 1st piece and $y for the 2nd/3rd/etc. So, my question is, how do I set up multiple flat rates (because of the different size flat rate boxes). Can this be done?