Full tank of gas will also help dilute any water in the tank. Sta-Bil is a must, been using it for years on all of my power equipment and it's cheap insurance.

I have the Battery Tender that can handle regular and Gel Cell batteries. I think it was about $45 on Amazon. It charges then floats (currently hooked up to the STR). You can leave everything hooked up. Has 2 indicator lights for charging and float. Well worth the money.

But a couple of cans of Damp Rid too. Open them up and put them inside the car.

Don't put any rodent bait in the car, rather use traps in the garage. You don't want to attract them to the vehicle, rather pick them off from the general area.