The curved hip area was exactly what I was going after and I can make that section strong, light, and exactly form fitting without any screws, bolts, or sharp edges. That part should be pretty easy.
It is the frame portion that I'm trying to figure out what design might be best. Flat, curved to match the shape of your back, or like the modified Harrier pack that you just posted that arcs away from your back (guessing for improved air flow?) ?? Sounds like you are going after the last route, curved away from your back. Supplies should be in on Monday to start the new tooling concept. Should be a fun project!