For the first time I'm thinking of putting my classic out side this winter to make room in my garage. I'm in Pa. and some winters we get average snow amounts last winter 2 " I was thinking of putting the car on 4 cement square slabs with 2 car covers on it but what would you lay under the car to stop moisture from affecting the under side????????

Plastic or plywood.

I'd put a soft car cover on it and then a tarp over that. Beware that wind can cause car covers to wear thru your paint on the fender edges

Pretty damp in PA & NJ as I recall.
Stored a car in a storage facility one winter when I lived in South Jersey; it was so damp in there some of my tools rusted.
Outdoors was even worse.
Anybody near you have a garage you could rent ?

What about a storage bin/facility? May not be heated but its out of the weather, shouldn't cost too much for a basic unit. Monthly rent may suck, but its cheaper than paint repair (moisture damage, tarps doing damage, etc, etc.)

Looking at topside's post, I would have to say it depends on how well the place was built. Is there ventilation? The only time I had moisture problem here along the swampy Gulf Coast was when I rented a bin made out of corrugated tin with a dirt floor.

The one I rented was a nice place: block construction, concrete floors, think it was a composite roof.
Typical of the large places you see for home-stuff storage.
It didn't damage the car, but the condensation on my stuff was worrisome.

Check into what indoor storage costs. When I did it here it was around $250 for the winter. Once your car is in that's it till spring. One place I used had a quonset hut and pole barns, the last place was a warehouse with several hundred cars parked in it.

hi

hi if this is a nice car DONT store it outside ,

damp rain days will get in no matter what you cover it with !

sun in the day and cool at night = condenstion in the body and engine trans rear ect !

also Mice will get in interior headliner ect !

put it in dry storage area only !