What i was planning on doing was to leave the shape however it came out and add two bulkheads and cap off the center with canvas and resin to seal it up. Using each end for a bit of storage. The parts i cut at 9" high at the center and if i'm right it would be fine for floating downstream on an easy day. I was actually going to make a steel tube frame to go between the pontoons and attach a regular plastic boat seat. Add a couple foot pegs or bar and be done with it. Much like one of these
http://www.cabelas.com/product/Creek...h-All+Products
This boat (which i ordered today when i found the sale) is what i was going after but for this price i don't think it's worth the effort to go through making the boat myself.
Here are a few pics of what i was playing with.