Not sure you need a tarp underneath , but you should definitely put something non-porous under the tires. Earth, asphalt, concrete will all leach the emollients from your rubber. A good low cost option are the large size, cheap, nylon cutting boards found in dollar stores. Don't use regular wood (like 2x10) as it will allow the leaching as well. Don't forget to cover the tires too.
A democracy is two wolves and a small lamb voting on what to have for dinner. Freedom is a well armed lamb contesting the vote.