I usually store a car on my enclosed trailer. I have a solar charger for the trailer battery and use it for the car battery.
I have had two problems: One is that the roof leaked. The other is that the brass on my Model T oxidized faster that it would have in a garage. That may have to do with the air quality where the trailer is stored. So now my Star spends the winter on the trailer when I need the garage space.
I have a 20' enclosed aluminum trailer. My trailer has a plywood liner and also a vent which seams to keep down any condensation or sweating...We are snowbirds so I have cars and garages both in Arizona and Washington and the trailer seams to be a great dust free, mouse free area to keep one car....One fall I used the Car hauler to help my son move to Phoenix from Washington, we had the trailer loaded mostly with large book shelves and books, anyway we had to hang back in Leavenworth, Washington so my wife could get treatment, so this took to the middle of winter before we could head on south, so I hung a 150 watt light bulb in the trailer and kept the snow shoveled off the roof, I was a little worried about the books and moisture but their was no problem at all.