To keep mildew out of your boat whether you park it in the garage or outside under a cover you need moving air. The solution is to go to Walmart and buy one of those small, compact plastic housing fans. Place it in your boat and put the power selector on low and forget it. Been using this for years and works like a charm. Cost of the fan is about $5.98. I use a splitter on the the extension cord running to my onboard charger and plug it in.