Last summer, I made over 100 boxy bags. I used laminated cotton mostly by Moda and other name brand designers. In fact, I have bunches of this and zippers left over if anyone wants to help me destatshing
. The one hint I can give you is to use a zipper that is at least 3-4 inche's longer than the opening. This gives you room to work and when through sewing the zipper, you cut off the end and sew across. Any questions or for fabric or zippers please PM me.