I just finished building a wood-strip high-deck Night Heron, and ordered a custom seat from Joe Greenley at Redfish. It took him about a week to make it, and it just arrived this weekend. It is sculpted from a thick piece of closed cell foam, and has hip pads and and a backrest built right onto it, and a rear extension that goes under the coaming and presses against the bulkhead. Joe's website has instructions for the measurements he needs to fit the seat to your boat, and how to measure the hull cross-section if he's never built one for your type of boat. Anyway, I compressed it a little to get it down into the boat. Then I pushed it to the rear of the cockpit against the bulkhead, and popped the hip pads under the coaming sides. It fits the boat so well that you can't slide it a millimeter in any direction. Sitting in it makes you one with the boat.