I bought a car jacket for mine.
Car Jacket Car Bag

It's pricey, but it has the benefit of totally enveloping the car. It's like a sleeping bag for your car, and zips all the way around it. It keeps critters out. It keeps moisture out. It also comes with some bags of re-usable "dry-sweep" to collect any moisture that gets in. Put one pan under the car (inside the car jacket) and one pan inside the car. Leave the windows cracked a little. You can even run the power cord for your float charger in at the end of the zipper.


Also, I put 2 foot squares of stiff foam insulation under my tires for the winter. You get the stuff from any home repair/supply store. It's cheap, about $10 for 1/2 of a 4x8 sheet. They should even cut it into squares for you, if you ask. Just lay them out on the car jacket, drive right up on them. No flat spots after 90 days for me.

Foamular 2 in. x 4 ft. x 8 ft. F-150 Insulation Board - 270895 at The Home Depot

And as a side bonus, the 2x2 pink insulation squares make great door bumpers during the rest of the year. My garage is really narrow, so it's almost impossible to get out of the car without hitting the wall. Door bumper to the rescue! LOL I just lean the square against the wall where my door would hit. Easy peasy.