hmm. the biggest thing is propulsion- i think you are planning on just a prop, although it could use the tail movement... that would be a challenge. i would say the hardest part of getting it to be dry hull with the wood, is were the linkages from the servos, and the prop shaft exit the hull.

on the other hand, a water tight cylinder is expensive, cause it takes time to build one and they are made by hand, in low numbers. so i suppose that making it dry hull would suite your needs better.

benthehen