I think you might want to explore internal frame packs that use a carbon fiber support system too. As for dual purpose, I think I'd rather have a chair or stool to sit on too, than a cot to sleep on.

A chair or stool should be lighter, and possibly easier to integrate into your design.

While a chair may seem like something that's so simple it doesn't need to be considered, it's actually been a very difficult problem for backpackers to solve.
The issue has to do with weight vs utility, and so far no design that I know of has hit the mark necessary to make it onto many backpacker's gear list.

For me, even a backrest would be a wonderful addition to my gear list, especially if it was dual purpose and added no weight to what I already carry. A backrest would obviously need to be built quite similar to a pack frame, so it might be done with some clean and simple design changes.

Let us know what you come up with...
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