My Moomba is stored outside my house and under a cover. Every year when I get the boat ready for the summer, the vinyl is covered with a blackish mold/mildew. Does anybody have any relatively "easy" way to safely remove this mold/mildew without harming the vinyl?

Any ideas for preventative measures that can be taken to reduce the amount of mold/mildew that grows on the vinyl over the winter season?