Have you seen Ken Rassmussen's article on customizing kayak seats? It can be found at: http://www.isomedia.com/homes/gadfly/kayak2.htm

His suggestions include those you've already seen here -- drilling drainage holes in the middle of each cheek depression and using them to guage your seat thickness. I think I left somewhere around 3/8" under my cheeks when I carved my seat. You don't want to sit too high -- it will raise your center of gravity.

Ken suggests using velcro to fasten the seat to the hull -- this system permits cleaning out the grunge that will collect under your seat over time (it smells!). He also suggests carving a narrow center channel in the bottom of your seat to permit water to drain easily from the back of your seat to the front, and from under your seat. I used spray on contact cement for my seat, and regular contact cement for my hip braces. Both work well and are still sticking after one and two years of moderate use and abuse. You can get velcro with a self-adhesive, but I don't think it will be as bomb-proof as regular contact cement.

If you go with velcro, take his advice and glue a small nylon webbing tab to your seat to facilitate pulling the seat off of the hull -- it makes it easier to remove the seat. I used the same system for my hip padding, since I wanted to encourage my daughter and wife to use the boat (their hips are wider than mine). I used 4" velcro to attach the carved hip pads to my cheek plates. The small, projecting tabs make it easy to remove and replace the hip braces.

You can use left over foam to create a bottle holder, sponge holder, or anything else you want in the cockpit. Some people cover their foam with neoprene or speaker cloth. I was going to do that until I shaped my seat, sanded it with 100 grit, and found it quite nice looking and feeling as it was, without any extra padding or covering.

Jim