If you know some one who works with metal, aluminium would be a better option. When I worked a a sheet metal shop I made the deck support frame for a couple of boats out of aluminuim and was able to use thinner plywood for the deck, which saved weight. Kens boat is a good project to look at for some ideas, though I am not sure how easy it will be to make a deck that you can remove quick and easy. Keep us posted on how it turns out.

Lotta ins, lotta outs, lotta what have-yous