Lots of opinions on this one. I guess it really depends on where you live and the elements that your coach will be exposed to. Where I live, it gets very hot, so my instinct told me to get a cover. Unfortunately, it also gets windy every afternoon.
The owner of a Greyhawk stored behind mine, purchased one of the Calmark covers. Very nice cover, guaranteed not to scratch. After two months, he took it off. Scratching wasn't the issue. It was wearing right through things from flapping in the wind, and he kept his very tight. The front cap was dull around all the edges, the texture on the rubber handle next to the door was worn smooth, and the upper rear corners were worn down. It would be nice to keep the sun off of it, but you have to choose what kind of damage you want.
If you live in an area where the wind isn't a factor, then a cover could work well.
Brian, Mary, kids, beagle - Moose, and mutt - Maggie.
2012 Greyhawk 31FS
2013 Ford Explorer Toad