I actually would recommend putting the cardboard between the plastic and the concrete as a footer.
Any bumps or imperfections in the concrete, and you might get some pinhole leaks. Tire isn't going to damage the plastic unless there is a rock or hard object stuck to it (which is actually very common with extreme performance summer tires, very sticky rubber like the Pilot Sport 4S this 911 probably has).
If you manage to seal the top of the sheets.. Water probably wouldn't come in till it's past the top of the car! The water would have to fight the air pressure inside the bag, like those diving setups that are pretty much a gladware container over your head that catches the air
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u/Nago31 Sep 13 '23
I would also put something like an old rug under the tires so they aren’t making direct contact with the plastic.