Marine 31 Mildew Remover Combo Marine 31 Mildew Remover and Mildew Guard provide a solution to a common problem that plagues all boaters  mold and mildew growth on vinyl surfaces. Removes stubborn mildew stains from virtually all surfaces of your boat, including vinyl seat cushions, non-skid, rubber fenders, and more. Marine 31 Mildew Guard forms a durable coating that protects vinyl surfaces, keeping them looking and performing new for years.