"The top edges of the seat are bolted to the cheekplates with (2) 1/4" SS bolts.  I haven't yet added any padding. I might add some 1/8" minicell for "cheek grip" but it doesn't really need padding for comfort.

I added a generous "pleasure pod" in the mold that when leaned, really keeps your "top leg" from falling down. I glued in 2 commercialminicell hip pads, but I didn't leave quite enough fiberglass at the top of the seat sides for a gluing surface--I need to do some customizing there."

This is Shawn Baker's quite beautiful strip built Guillemot cockpit.  He had made a fiberglass seat from a mold he cast of his posterior.  The complete instructions are:

http://www.geocities.com/shawnkayak/seat/