Clean it before it goes away, not after it comes out; a season of dirt put away comes back out as a season of mildew. Let every piece dry completely, seams and undersides included, and air dry only (heat distorts panels). Store canvas in its boot or bag, roll clear vinyl (never fold it; a crease is permanent) on a warm day of roughly 60 degrees or more with soft cloth between panels, and stand cushions on edge. Keep everything somewhere cool and dry.