Covering works for us ....
Using a fitted RV cover is much different than just using a tarp. We have a semi custom CalMark brand cover, that fits really well, and has not caused any wear or moisture problems. Our trailer looks much nicer than other similar aged trailers in the same storage are that are not covered. We get it nice and clean before we cover it, and when the cover comes off it is shiny clean and ready to go. Also don't have to worry about minor leaks, mud wasps, or other flying critters ....
Bill and Kate
Stone Harbor, NJ
2005 Jayco Jay Feather 29N (Salty Dog House)
2005 Ford/Quigley 4x4 E350 Van 6.0 TD (Moby)
Reese Pro Series SC Hitch