My two cents, I also thought that covers were a waste of money. I used to live in the desert of Southern California and heat and sun fade were the worst things down there and a cover at that time would most likely itself be wrecked in a season. Now living in North Idaho and keeping our trailers on our property with trees everywhere, I use a cover because of the damage accumulated tree bits, leaves, twigs, etc, DID cause to our 5th wheel by accumulating and keeping water in those spots.
And with our 2009 travel trailer a manufacturers defect was found after water had frozen in the incorrectly attached roof to front cap causing a leak when it melted that flooded the walls and cabinets on one side of the bedroom. We got that fixed, $1200.00 and a year later bought a Wildcat Maxx. I had a cover for that '09 trailer too, after what had happened, never another water issue.
As I'm not willing to "test the waters" again I keep it covered unless we're on a trip! We plan on building covered parking for the trailers to keep off, snow, tree stuff and such. But until then a cover costs way less than another repair job, that wasn't covered by our extended warranty! But that's another story altogether!
So I'm on the 'get a cover side'.