Oh, no need for sewing. Use triglides, like these and nylon or polypro webbing like climbers use, or that are used in cargo straps. Increases your versatility, can be set up in a minute or two, and doesn't require any understanding of needle and thread. :P

I currently am using a LONG length of 2" flat nylon webbing as the strap for my bag of tricks, and it just held together with several triglides. I'll see if I can get a picture of the sling tomorrow, it will show what I mean better than I'm probably explaining it.