For most of the year, it is a rinse and a gentle wash, with the cover still on the boat. Brush off loose dirt, rinse with a hose, wash with mild soap and cold water using a soft brush, and rinse until the water runs clear. Let it air dry completely before you fold, roll or boot it. Rinsing about once a month is the most effective thing you can do: mildew grows on dirt, not on the fabric, so removing the dirt prevents the problem. Avoid any cleaner with a degreaser.