Maybe some modified variation of a Mill Creek type seat?...It fits in the cockpit but you might be riding a bit high.  I have lower back problems but I find that with a piece of mincell foam on the back of the seat and keeping it a bit reclined, the Mill Creek seats are actually quite comfortable over extended paddling.

Chris 

Thanks Chris for the suggestion.  Nice looking boat by the way.  It is important for me to sit as low as possible, so the Mill Creek type seat is not ideal.  I made the 16 by 4 inch plywood panel as I mentioned earlier, and think this may be the solution.  It is easily removable, and if I lose it, so what.  I can make others easily. 

I don't really understand how people can paddle sea kayaks for extended periods without real back support, and I really don't have back problems.  I have always been uncomfortable in boats with no back support--even as a child.  

A couple of months ago, I made a truly wonderful folding seat for a canoe, only like a knucklehead, to sell the boat and the seat along with it.  The seat was better than anything I have seen on the net.  Might have to make another.  

I tend  to lean forward away from the backband while I am paddling. This makes it easier for me to develop the twisting motion at the waist I find necessary to develop more effortless forward strokes that can be sustained over a long time.

When my back does get sore, I like to get relief more from stetching out my legs, feet off the braces and leaning forward as if to touch my toes.

I have also found that stretching and any exercise that strengthens the abdominal muscles reduces my back pain generally, in any activity. Stretching, especially when I have spent some hours sitting in a d&mn kayak:) Stop, take a break and stretch a little.

But everyone is different, and there are different strokes for different folks!

Possibly lowering the seat a bit might be also be an adjustment you could make that would help you feel more comforable with existing backband?

I have been experimenting with plywood back support panels, and found that an ideal size for me is 3/8ths thick plywood 16 by 5 1/2 inches.  You insert the panel in front of the back band and just behind the mini cell seat.  Doing a scientific comparison, using this back support panel is 1000 times better than not having one.  Problem resolved!

The Creature Comfort seat comes up higher than the Rapid Pulse back band and give enough support that I was able to spend over 8 hours in my Wood Duck 12. It's still low enough profile to work with my spray skirt.

Laszlo

The objection to high seat backs in kayaks is that they seriously degrade stability.  Narrow kayaks work because you pivot at the hips, letting the kayak wobble a little from side to side beneath you while you unconciously balance.

If you have a really tall seat back, the seatback becomes a lever, pulling the kayak over with you as your body topples from one side to another.  Wide, stable Mill Creeks can stand to have taller seats.

But back bands are always quite low in traditional sea kayaks.  (And, in racing-type kayaks, are lower still or nonexistent.)  The Creature Comfort Seat's design has excellent lumbar support, but it's low enough not to degrade stability much in a touring kayak like the Chesapeake.