I've almost finished 2nd iteration of a skin on frame surfski (well, a de-tuned surfski) and the canvas bucket I've done for that might be worth considering. The one in the first iteration has proved comfortable for hours on end, and I've been thinking for a while that it might be an option for stitch and glue/strip construction as well: hung within a plain straight sided bucket. There'd have to be some careful design to minimize wasted volume, but construction would be easier and probably stronger.

Apologies for poor quality of photo:

(It will be prettier when I've coated it - made a mess of gluing with polyurethane adhesive/sealant).