back in the '80s I was seeing ads for The Car Bag which had a small compressor that kept the clear car bag inflated
You lay out the bottom, drive the car onto it, the rest of the bag seals to the bottom, you turn on the compressor and filtered air inflates the bag, There's a one way valve on the other side that keeps a constant pressure.
The idea is still around
http://carcapsule.com/