I have not had a problem with tires cracking.  I have a 1961 Oldsmobile that I replaced the tires after 25 years and they still looked like new (they were just to old).  My cars are kept in a garage at a constant temperature/humidity.  I do not cover my cars in the garage. 

  I bought some Kuhmo Ecsta's from Jegs for my 96 LT-4.   285zr40-17's for 126.00 each, Jegs ate the shipping, then to mount, new valve stems and balance was 64 for the pair.  Just a thought-flandy