Forgot to mention a couple of tips. When I did trips, most people showed up already WELL on their way to dehydration. It's so dry that you don't really sweat, so most people don't realize what's happening. Drink a LOT of water - 1 Gal/day. Signs of dehydration are crankiness, headaches, etc. The best sign is the color of your pee - if it's yellow, you're dehydrating. Coke and beer are diuretics, so drink water.
Also, most people tend to try and do too much and drive too far. Make sure you plan down time to just hang out in the shade somewhere or dilly dally. Makes a BIG difference. Sure, you may not see everything the guide book says you should see, but you'll enjoy the trip much more.
