I usually lift the rear end of my car with a jack when its in storage or sitting because the slicks will develope a flat spot if the weight of the vehicle sits on the slicks for an extended period of time, many racers store there cars by lifting the rear weight off the tires and over inflating the slicks.
I always have mine in the air for any extended period of time, front and rear. I run Goodyear drag front tire and Mickeys on the back and have had other racers tell me about having flat spots on the front tires as well.
My ET Street Radials are still good after 3 years, about 70 runs and 5000+ street miles on them. I know they are still good because I got my best 60 ft time (1.64) last time out. When not racing for an extended period I put my street tires on, lay the ETs on their side and drop the pressure to about 5 psi. Otherwise I leave them on the car and drive it often.