All of our boats are out in the elements and are going to be exposed to moisture frequently. For that purpose you need to coat all the wood surfaces with a few coats of spar urethane.
Use exterior grade plywood for the decks - but you will still have to treat it - exterior grade does not mean waterproof. You can use 3/4 inch if you want but 1/2 is plenty for most situations.
If you can afford it use aluminum for the framing. If not just use whatever dimensional lumber you feel comfortable with, though 2x2 is adequate and will save you half the weight vs. 2x4...
Use exterior grade plywood for the decks - but you will still have to treat it - exterior grade does not mean waterproof. You can use 3/4 inch if you want but 1/2 is plenty for most situations.
If you can afford it use aluminum for the framing. If not just use whatever dimensional lumber you feel comfortable with, though 2x2 is adequate and will save you half the weight vs. 2x4...