Chas, I'll incorporate the painter-keel into my plan.
Anne, that's an interesting thought. If I'm going to be possibly using a poly skin, why not make the structure from synthetic materials as well... you could go super primative or you could go completely man-made, and everything in between. Perhaps some kind of vinyl would work--you need an 6' - 8' length, I believe, to make the ribs.

Now I wish I hadn't sold my papasan chair back in '04. I could have covered it with a skin and set off down the river. ;)