I park on concrete and use wood under each tire. As a suggestion, I go to Home Depot and look in their scrap bin for half sheets of plywood (1/2 ") and will buy that about every three years (sometimes you can get roof decking which is weather proofed and it will last longer). I then cut it to fit either the single front tires or leave as a 1/2 sheet for each side for my rear duals. I also keep the tires covered with sun shields (I bought mine at Camping World).
Dave and Karen -- '02 Ultimate Advantage 36 C, 350 HP Cummins, Allison 3060 Tranny
'07 Ford Escort, Brake Master 4160, '13 Ford Edge, InvisiBrake