Jim:

I built a fiberglass seat using a sandbox by sitting in it, using plastic wrap in the impression and then glassing this. easy to enlarge the sides of the seat too. Mine is about 1/4" off the center of the hull at the deepest part of the cheeks. I used 3" and 1" minicell on the perimeter of the seat to support it. maybe 6 - 10 layers of 6 oz cloth with most of it being spare scrap material. make sure the topmost layer closest to your butt is a single piece though to keep it nice to sit on.

Also, I use a rapid pulse backband via CLC.

Pete czerpak Albany, NY