Just an observation-
We store our 5th wheel in a lot with nearly 200 RVs. I see new RVs come in to be stored and the owner will use a cover for about a year and then you never see the RV covered again. Over the 20 years we've been at this lot I've seen no fewer than 40 RVs where this is the case. We are in southern California within 6 miles of the ocean so weather is not really a factor other than lots of sun and fog in May and June.
I'm guessing it becomes too much of an effort to put the cover on versus the benefit derived by covering it. Our 5th wheel has been uncovered the entire 20 years and it shines up like new when washed and waxed. The EDPM roof is still in good shape. I do wash the RV at least twice per year and wax it every other year.