Tom,
I've mentioned it before, but I spray everything down with Mean Green Mold 
and Mildew Destroyer. It isn't available everywhere, but it sure works well. I 
let it set for about five minutes and then I use an auto wash mit with warm 
water and tide. After rinsing, if there are any marks or areas that didn't clean, 
I go back and use soft scrub with bleach and a scotch brite (green) scrubbing 
pad. Just enough abrasion to remove the crap and leave the gel coat intact.

Rummy