Just finished making 2 of these for my scouts. We used "kid" sized bags, which translates to about 3/4 length for the boys these days.
Remove the zipper, and fold the bag in half like it was zipped up. At the top of the bag, sew the gross-grain to one layer only, making a pocket for an optional pad. The 3 remaining sides, sew gross-grain to both layers. Shock cord the gross-grain channels, and put cord-locks on the ends.
Hang it off of "quilt triangles." I make mine from 5' of rope, with 3 overhand knots placed at strategic locations.