I leave my vents open to help eliminate moisture build up and the possibility of mold growth. And I never cover a wet grill. Oh also once I find that a grill cover doesn't stop water it goes in the trash. The best covers I've found for keeping a kettle dry are KingKong covers available from Amazon. For my WSM the iCover is the only one I found that will fit and keep it dry. WSMs are really bad about molding so I check it frequently for moisture and always keep the vents open. Hope that helps!