: I am not sure whether I read it at Guillemot sites, but I did read an opinion
: that said DON'T make bulkheads of a solid type such as strips as this
: creates a hard spot if you run over a rock. Better to use a softer
: bulkhead that gives.

While it certainly can happen, it's not a big problem. If you want some flex, you can mount a rigid bulkhead using fiberglass, leaving a 1/4-1/2" gap around the rigid section. The glass tape and epoxy will flex enough to prevent any problems. I've seen pictures of rigid bulkheads with Minicel foam at the bottom and part of the sides, which allows some flex.

: Also, if one makes a bulkhead with a tight seal, what happens in if one
: leaves the kayak in the hot sun. BOOM? As a windsurfer, boards these days
: have screw seals to release hot air. Is some kind of air release valve
: available for kayaks?

Yeah, it's called "a pinhole hole in the bulkhead". Venting bulkheads is pretty standard practice. All it takes is a hole ~1/32" or slightly larger in each bulkhead. Problem solved.

: One of my kayaker friends said he was worried about condensation in his
: sealed bulkheads. ?????

It's possible, but the only moisture is going to be what's in the air in the compartments. Venting the bulkheads helps, but leaving the hatch covers loose or off is even better. Again, this is not a serious problem.