We had an ADCO Designer Series cover on our previous Class C. The fit was very good and for approx. $250.00 it provided good protection. It was also breathable, so no mildew etc.
Ensure that all sharp edges are wrapped to protect the cover from ripping. ADCO also have a feature of straps and buckles to tighten the front and back ends.
There was a good video on You Tube.
My concern was covering it in October and re-opening in January to head south and the possibility of snow or ice build up that would make it difficult to remove. Fortunately, that never happened.
We experienced no scratching or rubbing on the paint from wind flapping.