I think hysol is the same type glue that I tried, which was mcnett aquaseal glue. Too thick really, but it sticks everything to everything I have tried. Sil to sil, sil to tyvek, sil to cuben, cuben to cuben, so that is what I would use. Have not tried it on polycro yet, but thats next.
I am acutally going to make a couple of these bags similar to what you are doing. Square and clip corner technique with roll top.
You could just glue on some velcro for the strap or use some 1/2" grosgrain and a small 1/2" side release buckle.