I've heard good and bad about both. Personally, I do not cover the whole camper. I do put my wheel covers on and I have an ac cover that goes on for the winter months too.
What I have heard is that a complete cover traps moisture and can create other problems.
I was also told if I do not cover, be sure to keep up on roof inspections and resealing. I think that's good advice either way.
'97 Jayco Eagle 314BHS
'03 Tahoe LT 5.3L