I utilize two covers for the different seasons. I use a full cover brand name "expedition" which are sold by length. If memory serves me, the one you want is the up to 26 ft. That is my winter cover. Fits very well, but not a cover you want to put on and off often. That cover is for winter storage. Summer I use a white poly tarp found on the net, which serves two functions. 1. White doesn't look so odd being the unit is mostly white anyway.
2. White reflects heat very well. I purchased a 20ft by 10ft and just use a good quality parachute cord on bungies near the bottom four corner connection points. That size just about covers the coach roof area, and keeps debris off as well. However, note that my parked location is shielded from any high winds, so in my application, the white tarp won't sail.