If you can afford it, inside storage is always going to trump outside. Mice can be controlled, the weather not so much. The mice are also outside so no advantage over inside storage. Rodents should be way down on your list for storage choices.
Snowfall in the TC averages 48" and 10 major snow events/year. It doesn't all accumulate. I tend to remove snow from my trailer as it piles up. Keeps the roof and ceiling from compressing. I use a roof rake with a pair of wheels on it. It rides above the roof surface and doesn't contact the roof. I operate it from a ladder alongside the trailer. It is a 30 minute ordeal. a few times a year.
A Class C RV will have a fairly stout roof structure, similar to my enclosed cargo trailer. I never remove snow from that.