I wouldn't as it's unnecessary. Those roof top mount ACs are designed for strong winds, blowing rain, ice, and snow. I'd think that what your neighbors do would be the route to follow. Check out the back of any nearby RV park where they park the RVs long term...do those have covers? Do what they do, save yourself some effort.
Next spring, any ice or water accumulation should drain out where the condensate drains out. And unless you have a seal problem, none of it will get inside the RV. There shouldn't be much inside the AC anyway. I know with mine up in Fairbanks, I watched it as it slowly warmed up, and I'd have a trickle of water off the roof as it slowly melted.