Unfortunately, we are forced to park our coach outside, so we have always covered it. We have always purchased the Adco covers from Camping World. Do yourself a favor and buy the 3 year full replacement warranty, it is the best deal in town. We are on our third cover and it was replaced each time no questions asked, for just the price of the warranty. Our first cover ripped due to sharp edges here and there on the coach. I quickly learned that tennis balls come in handy to put over ladder and awning corners. Second cover just finally gave out due to the sun. The straps became brittle and ripped after 2 1/2 years.
They are a hassle to put on but I wouldn't leave a coach outside without one. Reason one, the sun beating down on your coach is brutal(at least here in AZ). No way around it and IMHO, even the best coat of wax with UV protection won't do as good as a cover. We use both FWIW. Reason two - a cover will keep your coach MUCH cleaner than leaving it out in the elements exposed. Even with our nasty monsoon storms, my coach was perfect when when I took the cover off. There was only a light coat of dust that was easily hosed off without even needing to wipe it.
We had a 38' Coachman DP that we just sold. We just purchased a 42' Monaco that I just ordered the cover for yesterday. Hope this helps.