Glad to see this thread it becoming very interesting and informative. Not that I'll be making a vest out of a backpack, but I appreciate the inginuity of those that gather, think and make airsoft stuff. Check out my drag bag:
Made out of an old CF sleeping bag (down feathers removed of course), used the fabric, the webbing liner inside the zippers, and the zipper cut to length, a 'pussie pad' sleeping bag foam roll up mat for padding, and the two cargo pockets from an old pair of CF cold weather pants. I tend to modify the hell outta my stuff as well, but this drag bag was a pretty big endeavour, and works great. Even used the same materials to make the shoulder straps to carry like a backpack.
Keep it up Mirage, always great when people post things they are making out of every day stuff.