Dan with the frame from his Kakwa 40 pack.
Apparently it’s pretty challenging as a DIYer to bend 6061 tubing without creasing it or causing wrinkles, and requires you to fill the tube with sand before forming.
Discussion
I really like the upside down U shape frames for packs, as opposed to the older way of attaching says of some kind to a plastic sheet, because it gives horizontally stability as well and helps prevent the pack from barreling (which is exactly what it sounds like)
6061 isn't nice for bending in general, 3003 is a lot easier to work with and I doubt the strength difference would matter