Hi All:
I too made a shooting table out of 2 sheets of glued up plywood. I too parked my car on the wood in the garage as GregSY describrd. This worked quite well,
One thing that I will suggest is that is that one drives two small nail into each corner on one side of the wood. This will prevent the wood from sliding out of place when one drives on it. Be sure to use plenty of glue! Trowel it on for 100% coverage. I prefer the yellow carpenter's glue. It may be an aliphatic resin type that can also be assembled dry and then heat activated. Of course there is always contact cement but thaat is another story!
Good Luck,
Franchi