Although I don't have a motor home, check out the ADCO covers from Camping World. I purchased the one for my Cherokee 274DBH and used it a few times. Problem with covers or at least this one is you can't run the air or the refrigerator with the cover on. Oh and those RV covers are a pain to put on, take off and require you to get on the roof to roll them out on the install.
What I'm preparing to do instead is make a custom cover out of 1 5/8 chain link top rail. I went here:
Canopy Fittings and Portable Shelter Connectors
and ordered the fittings and tarp to make a cover to fit over my camper. I am planning to go to a local fencing company and have them cut the center sections and legs at 10' each. Since they come in 24' sections, I'll use 8 of the leftover 4' pieces cemented in the ground with the tapered end up for the legs to attach to. I used an online pitch/run calculator to get my measurements right so in the end I'll have a nice cover that even covers the slide when its out. You can add pretty much whatever type of screen or tarp material to the sides for more coverage as you have funds available. Since you don't have hurricanes in your part of the country, this should work well for you and that company is in southern California so you might be able to drive there and get it cheaper without paying shipping. It will cost me around $800 total but cheaper than a portable cover at $2500.
Hope this helps.
2015 Cherokee Limited 274DBH
2000 F250 CC SD V10 4X4 8' bed, 4:30 gears, SCT X3
2007 Mustang Convertible V6 - Lots of GT mods
1965 Mustang Coupe I6, 3 spd. manual
1963 Thunderbird Landau 390