We use a 20' x 30' silver tarp only during the winter. Using 1" ratchet straps on all the grommets keeps it from flapping in the wind and it protects the trailer from tree sap, falling small limbs, etc. Obviously it would help prevent leaks as well, and not totally covering the sides, there is plenty of air circulation to prevent condensation problems. It's easy to loosen one strap if you need to get into the trailer. I got the tarp and straps from Harbor Freight and total cost was less than $80, much more economical than a cover if cost is a consideration. I feel that it works just as well and the tarp held up very well, can't even tell it has been used.