Mice/rodent proofing a camper

I'm still trying to picture how a mouse gains access to an RV. As far as I know they can't really jump and assuming there are no trees/shrubs/etc. next to the coach, the only way up would be via the tires or the tongue jack (assuming a TT). I can't imagine any way a mouse could climb the smooth steel sides of the tongue jack, so that only leaves the tires.

So, if the mouse climbs a tire, now what? Can't get to the frame. Maybe could make it to the axle, but then where from there? I understand that they do get in, I just can't quite see how?!?!