i bought a dust cover from Griot'sGarage. they have a supplier make one for them with their Griot's logo. it's nice, but unless you're going to be opening the garage through winter it's a waste to have it.
my garage rarely opens from dec to march... so i haven't used it much. lol
you can buy them from griots or autosports catalog. same thing.
Car Care, Detail Supplies, Garage Organization, Car Accessories - Griot's Garage 800-345-5789
AutoSportCatalog.com - Products For Everyone Who Drives! 800-953-0814