Has anyone ever thought of this: Why doesn't someone create a shaped bear cannister, say a kidney shape in cross section, with fitting lids - with a cross section shape to match your back. Larger than normal, shaped to fit inside a frameless backpack of, say, 45L volume internal, and this would provide a rigid internal frame for all the gear and waterproof it, and float it for river crossings? Taking it to an extreme, you could have a bear cannister as a small (e.g. 30L volume) pack with fittings and foam on its own for a backpack, as long as it was shaped in cross section. In my part of the world we don't get bears, but I've always wondered why you guys carry your bear cannisters on top of or outside of the pack instead of integrating it, especially as part of the frame, as most seem to then rely on rolled sleeping matt for frame and a separate bag for water proofing, as well as the bear cannister.
I've had a lot of experience in building competition white water boats in carbon and other more exotic materials, so I know such would be technically possible, and with appropriate foam cored technology you could keep the weight down to a fraction of a solid resin layup. Every time I see the "ideal" cross-sectional shape for backpack (e.g. Aarn website) I think about this sort of thing.
A thought, anyway.