I have never used a cover, whether stored in or out. Since I'm new to seasonal camping I asked the owner a couple weeks ago for his take. He said that unless you get a custom cover made specifically for your individual unit, the covers invariably cause damage to the roof and the sides. Just can't get them cinched down tight enough. Owner has managed campgrounds for more than 20 years.
I will not be putting a cover on my trailer.
Al & Karyl
'08 Sunset Trail ST29RL