I'll second this. Per Bill's recommendation, I looked up MDO at my local yards instead of marine plywood, due to the expense and limited availability of the marine stuff.

Every yard I talked to referred to MDO as the "highway sign stuff" (I'm paraphrasing). If the stuff will survive several upstate NY winters without significantly deteriorating, I'd expect it to survive a few hours in the water each week when used inside my kayak.

: MDO is fairly high quality plywood with a fiber lamiminated to each
: side. Think about it, most signs made from the stuff are outside
: for years, works fine on kayaks. Btw, the fiber surfaces finish
: really nicely, though you get a tan colored wood, almost looks
: painted. Oils well too.

: Bill H.