I have been storing a summer vehicle that way for 31 years. Been working fine. Mice is the only issue here on the prairies. The shop isn't completely mouse free. Never had any get in a vehicle. Caught them before they could I guess. Using a couple of bars of Irish Spring Soap in the Vette. Mice don't like the smell. Some swear by it. They never had mice trouble. First year for the Vette, have to try something. But had a guy tell a friend in Bismarck that he had a mouse take a dump on the bar of soap so he doesn't use them anymore. I don't like the smell of Fresh Cab in my car. OK for the motorhome. Some like dryer sheets but they need replaced every month. I'll will be checking the Vette once in a while.
Same issue here. I use the dryer sheets and Irish Spring in the car and under to hood. On the floor around the outside walls and under / around the car and Hummer is a combination of Irish Spring chunks and mothballs.... The smell in that garage could make a goat puke.
I use an electronic noise maker plugged into an outlet on the wall too. Not sure what's actually working to keep the little Bas***ds out, but so far so good for the last 4 years.