I am storing mine in the garage, but that is a fairly dusty space, so I have put over it a modified cover.
Lucky me, I found at Goodwill a brand new cover ($25) designed for the small R-pod camper, which turned out to be way to large. So, I broke out the sawing machine and retrofited that cover for the teardrop. Not the best looking seams, but it does the job.
the other week I left the camper for four days in a campground in FL, while I was offshore, and the modified cover worked just fine, it keept all the bird poop off of the camper.