I made a mockup of the hull, sat in it and tried to determine how much space I needed for a comfortable and snug fit. I clamped a couple of woodstrips in place and moved them around until I had enough space at my knees and at my feet (with boots on). Those two places got transferred to cardboard, and that determined the design of the deck.
Beneath the mockup is the form placed at the knees. As Bill writes it gives quite an interesting transition around the cockpit. (70 deg. twist done in only 50 cm) I placed a "crossmember" below deck just behind the cockpit (right where the coaming recess is located), and used the crossmember to add some strenght where I clamped/screwed in the strips with the most twist. Ill use the crossmembers anyway, as my reardeck is completely flat!

Gennie
www.byg-kajak.dk