If you store you RV outside for long periods, you should consider a durable all-weather RV Cover like this one.
The folks at EmpireCovers.com asked me to test and review their waterproof Premier RV Cover. I waited until it had been raining for a few days to see how it performed. The water actually pooled up on the roof of my RV which was a clue that the waterproofing was working. Overall, it performed pretty well as you can see in the video.
If you are considering a cover for your RV, travel trailer or fifth wheel do you self a favor and invest in a cover that will last you many years. less expensive ultra-thin lightweight covers are intended for short term use and simply won't hold up to long term abuse by mother nature. Invest in a quality cover that offers the maximum protection and you will have it for years and years.
You can find these premier covers on Amazon. Here's the link to Amazon if you want to see what's available for your RV.