Great ideas. I just got a TI, and I'll be sailing around Salem, Massachusetts. I've only been out a few times, but I see why you say it's a wet ride.
I love to tinker, and I've been thinking about adding hakas. I'm leaning toward simple, light wood construction. I just had an idea about another material, and wonder what you guys think...
This stuff is used to make lobster traps. They stay submerged for years, and are roughly used on a daily basis. I've also seen park benches made from the stuff, so it is stiff enough for that application as well. Light weight, maintenance-free, and fairly cheap based on what I've seen from a quick look online $75 plus shipping for 15 ft, 2 ft wide. It weighs 10 pounds. It's vinyl-coated galvanized welded steel. You work it using a brake for bending, c-clips for fastening.
I think you might get away with just bending a "hook" the full width of the haka at the front, plus a right-angle bend at the back to hold it against the back aka. Curl the edge under for a nice comfy seat, and to add some stiffness. If you need more stiffness, a wooden dowel could be added to one or both edges, inside the curl.
What do you think?