Thanks all for the replies.
There are a couple of feral cats on the property - I see them on my security cameras almost daily. We have some fox, too. If not for them I'd bet things would be a lot worse.
I do need to seal up the outside openings. There are only a couple that are big enough for a critter to get through - the biggest being where the power cord goes in. I've been meaning to do something with it for a while - I'm pretty sure that's where the mice are getting in. I know that's where the ants get in, but that's a whole 'nother rant.
Deflated footballs sounds like a good if-you-can't-beat-em-join-em plan. Give them something to chew on. I'd just have to remember it. Also spraying a lubricant to deter them sounds like it has promise. I'd like to think if I go out there and start it up more regularly they'd not hang out there. But, counting the RV, I have 7 vehicles. Except for the motorhome, none sit for more than a week. I have more cars than drivers but I make a point not to let them sit. Even so, every single car has busted open acorns and droppings on top of the intake manifold. It's crazy. So far no chewed wires, though.