Well Tin,
I tell you it is a **** shoot.....
If you don't cover it and there is any flaw in the roof, the Freeze/Thaw will pry it open and make it leak.
If you put any kind of a cover on it, you are making it a sanctuary for little critters that both carry out natural functions and chew on anything that is chewable (like the rubber seals on vents). Squirrels and raccoons are both real good for that.
So, I don't have an answer, but at least you know what you are dealing with. Where you are, I would try to figure out how to build a free-standing roof to keep the snow off.
Matt
Matt & Mary Colie
A sailor, his bride and their black dogs (one dear dog is waiting for us at the bridge) going to see some dry places that have Geocaches in a coach made the year we married.