I"m in the process of doing the same thing. I took a pair of my husband's briefs and have been experimenting with them. The only problem I have had is I used an old athletic sock to try out the design first and it was too bulky... don't want to draw attention to myself... I''m going to use some an old t-shirt and sew a pouch now that I have the basic idea. What type of opening do you have and is it stitched closed a bit, with a bit still open,or do you have a button, etc. I want to be able to take the packer out to wash the pouch.