AZ's hot and all... but it's SO dry. Where I live gets HOT in the summer, but fall, winter and spring are perfect (Sarasota). We never have that nasty dry heat, though... only the nasty humid heat :P

Anyways, its pushed 100 here before and I've parked in direct sunlight with a black on black SL500, also with my denim blue TT. If the seats are conditioned, it shouldn't be a problem at all. I only even use air conditioning about 2 times a year!

Tint helps even more... leather doesn't have to be unbearable, in any climate!

 

..cloth interior inserts on my roadster for exactly that reason