I bought an over sized cover from Northern tool.com for under $100. I use bungee cords at the front and back and hand clamps on the fenders to take up the slack. It does the job and I need to keep my rpod covered as it is parked under large pine trees that drip sap.
The sun is also a big factor as I live in Florida.
The cover works well as described. I've had several storms, and lots of rain. The quality is OK (the same as the cover I use for my truck). I know I will have to replace it every few years as I've had to do with high quality covers I've used on other vehicles.
I think all covers are hard to put on and take off with RV's. I use a ladder and put the cover on top of the vehicle. I then pull it down in front and back and pull it around the A/C and TV antenna. Once I have the edge past the AC and antenna, it is easy to adjust. I then gather material at the front and back. Then I make adjustments at the bottom around the wheels (I also leave the tires covered due to the sun).
Hope this helps others, it works for me for the time being. I've had my rpod since March.