: BTW I found that recreational kayaks
: such as my cheap plastic 12' x 29.5" with a hard plastic seat are
: comfortable because the seat is several inches off the bottom.

Jay's comment about the rec boat seats makes me think of the Phase 3 seat in my wife's Pungo. (www.wildernesssystems.com).

This seat has a kind of plastic flap covered with thin padding, that is "bolted" down at the back of the seat. You can pull nylon straps on the sides, and raise or lower the front edge of the seat.

When I paddle this boat, and my legs go to sleep, I raise them up in front for a while. Numbness passes. When it begins to get uncomfortble again, I move the seat the other way. It's quick to adjust, and each time I switched it, got another 15-30 minutes of respite from numbness.

It should not be too hard to rig something similar to a carved minicell seat. What's cool is that your tailbone area stays low all the time, helping not to raise your CG too much.