Chris I built one for my Mariner three yrs ago, one for my bro out of carbon/kevlar,and another for the North Bay I just finished. I can not say enough about what a better set-up than any other I have tried,minicell,thermarest etc. Comfort,boat control are much better. The effort on the thighs to lean the boat is much less and the hips don't have to be snug for the same amount of control/lean.

1. Make a dam for the front of the seat on the inside of the hull/under thigh or however far forward you want the seat. Same for back,3" behind butt is about right. lay plastic all around area and cockpit coaming.

2. make about 8 oz foam mix and put into large garbage bag. sit on bag in thick paddling outfit,wetsuit? opening between legs! careful not to have foam squish out onto self or boat.

3. keep adding foam as the confined foam will not expand or so that too much foam doesn't burst bag, also to ensure that as back and side of mold fill out you can push yourself up an inch by the coaming so the bottom of the seat is truly curved and not just squished out to the sides.

4. When enough foam has filled back,sides, cut it out(thirds) to sand and clean it up, reinstall in boat

5. pick cloth resin lay-up of choice and wet it , lay it , cover it, sit in it, get out when it gets too hot.

6. spend the rest of the day cutting ,cleaning ,coating the rough seat.

7. put it in.

I like to make the cloth wrap up the sides to be bolted onto a hanger from the coaming. there are some heavy biaxial cloths or maybe mat that form into a shape well without wrinkling too much. Make the edges of the mold rounded over so that the seat has a lip to add rigidity. Minicell foam and 3m 5200 secure the bottom and sides well to the kayak. A hole cut into the seat between the thighs makes a good place to put a pump, colored resin and colored finish coats work, varnish for colorful cloths can work.

go for it , it's worth it