Great responses from all.

Some of the main advantages of a sit on top are it's lower volume above the water line and therebye less windage, more ease of entry, and less cockpit volume (and water weight). This automatically means a low profile. For the sake of argument lets say about 7 - 8 inches at the cockpit vs the typical 12+ at the front and 9 + - at the back. ( I've never measured or sat in one so only guesses)

Now only if one assumes this, does a typical kayak w/ cutouts become too volumetric. And this low profile is where the buckling prob occurs. Easily mitigated by some extra layer of glass on the sheer (the vertical sides) to say 2 feet or so past the cockpit. Deck torsion would also be lessened by some extra layers of glass under the deck to the cockpit opening extending the same 2 feet or so.(I would just make them one pc).

I would think the U shaped cockpit is pretty desireable to keep onboard water wt down. And I guess it's probably not a big deal to put strips down to the deck when framing this area.(in relation to my recessed cockpit, it would be easy)

On glassing the i/s of the downturn strips, I would overlap the flange w/ the i/s glass, taking up the space of the duct tape to get a more exact fit and better sealing. And probably its a close winner to use outside seaming only. Easier to repair down the road.

The inner seat foam should be covered in say 1/8 in neoprene and glued in place or held in place by some wd. angle. Therefore removeable for the beach.

-mick