Mice have what amounts to cartilage for bones and can squeeze thru a 1/2 inch gap.. The only thing I know that they won't chew thru is steel wool. In my class C any openings get steel wool pushed into them, then I use spray foam to seal it up further. And the best deterrent is a outdoor cat. I regularly let my cats into my RV and let them roam around for a few minutes. I don't think the mice want to hang around if they smell cats. Only other thing I can think of is using something to put around the tires ( I think they don't like the smell of peppermint oil?) maybe a spray bottle and a few sprits every once in a while ? I would spray anything they can use as a way to get up into the vehicle. ( power cord, hoses, tires, etc...)