For the price we know we paid for a top of the line coach, I wouldnt fool around and go with a cover like this.
http://www.northerntool.com/webapp/w..._624662_624662
This not only protects the top from snow build-up, but will protect the sides from fading and blowing debris. I'd also put quite a few DECON Traps around the camper to make sure no pests use it as a safe haven to get out of the weather.
If you think about it, a cover like this although expensive, will last you years and keep your investment looking new for many camping trips
Pat