Splashhopper.. if you want to fix the leaks in your sportspal.. go pick up a tube of Sikaflex 1A (local United Rental sells it) and you can get it in various colours. Sand, aluminum, limestone etc. Or go into a marine supply and get a tube of Sikaflex 591 (white or black are your choices). Scrub the suspect area with brown scotchbrite, clean it with acetone, let that evaporate and then apply the Sikaflex. Should be no need to pull up the interior foam.
TC.. if you do go at the aluminum with sandpaper.. be absolutely certain that it is aluminum oxide paper! Personally, like I said, I'd check that thing for leaks... re set any loose weeping rivets and use it as is with the exception of at least cleaning up or replacing the wood. If you want to paint it.. strip it with TAL STRIP II or have it soda blasted. Then self etching epoxy primer for aluminum and top coat.