I'm trying to decide which type of plywood to use for flooring in an aluminum boat. I would rather not use the expensive marine grade, and was wondering if anybody has used AB or AC exterior, what thickness, and paint or stain (aka: Thompsons). Also, does it matter if it is pine or fir? I'm open to any flooring options, just wanted to get by a little cheaper. I don't mind replacing it every five years or so. Thanks for any input.