A while back, i came up with a simple pack design which used carbon fiber arrow shafts, in a rectangular box shape. Dyneema cord was wrapped around somewhat tightly all around the outside in a up down VVV. Since the back went against the cord, it helped distribute the weight a bit and keep the tubes off the back some, while keeping the back cooler.
A simple, lightweight silynlon stuff sack went inside to hold contents and keep them dry. Since the silnylon will not be rubbing up against anything abrasive, would last a long time.
It's not a great design by any means (if you fell backwards on it, might break somewhat easily?), but it was easy, relatively cheap, and very light.
The main problem was connecting the carbon fiber tubes together. I used puddy epoxy and don't think that was ideal, as out on a trip, one of the corners where three rods meet came apart (on closer inspection i had used a lack of puddy in key areas on that corner). I recently found this stuff that is a fabric, that you wet and wrap around things and is supposed to be very strong. Will try that out after re puddying the area to initially hold it in shape. I originally looked for pre made connectors at kite shops and hardware stores but either didn't find anything that would take 3 tubes with 2 at a right angle at top and one at the bottom, or connectors that were light enough.
David, i think, suggested some kind of homemade wood connector, which i might still try (but haven't yet because i have very little wood working experience, knowledge, or tools). There wasn't much interest in the project at the original time of mention, not sure if it was because people thought it a stupid/impractical design, or because i was a pretty new member, or a combo.
Ideally, i would have two extra tubes of carbon fiber connect in a V (or inverted V) between the top and bottom tubes that are against the back and which are connected to the pack straps, if i wanted to carry more serious weight (but that was not the intention of pack, is for UL and SUL loads). That would be hard to do well.
Well, tangent over.