If there isn't any saltcreep/ spray hitting the fans I find just basic cpu fans from places like radio shack work fine. I'm currently using a "TT" brand one that is fairly quiet, rated for the 20-25db noise range, so it isn't noticeable. 78 CFM for $10 seems to keep my tek at the right temp while inside my canopy.
If yours get sprayed once in awhile a more water resistant setup would probably be better.