I'm in southern California. Now, it doesn't get nearly as hot here in the summer as it does where you are, but we still easliy get in the 100's during august and september.
I bought QEW for just that exact reason. In order for me to dry the car after a normal wash, I would have the run around the car with two waffle weave mf towels. If I was fast enough I would get tons of water marks. It also gets very windy where i'm at that has the same effect. Also I can take my time drying with QEW, so I dont have to worry about adding swirls or spider web marks while drying. I do have a few other car washs but since this past summer QEW is all I've been using. I also add an ounce of FD to the wash bucket. I'll never go back to washing cars the old way again!