Thanks for all the great advice everyone.

As it stands today, we are almost forced to leave in the beginning of July, due to the fact that thats when most of us have our summer holiday. But like it was said, the car has an A/C, which I would say is almost a must that time of year, so it will probably be grand. Im gonna make a print-out of the thread regarding how to deal with the heat and such.

As for the cell-phone, our plan was to get a phone when we came down, as we plan on mounting webcams in the car, and use GPRS to upload images to the internet on our roadtrip website. We did this when we took a roadtrip around Norway this summer, and it worked really well.
But how is it with GRPS-coverage around the more desolate places of the states? And how about cell-phone coverage overall?

We are already set on going for an Expedition for our trip, and since gas-prices (atm. atleast) is 1/2 of what it is in Norway right now. We pay about 5-6$ per gallon, maybe more. So we're gonna be the guys who have a big grin on our faces when filling up the tank. ;)

Now, im not entirely sure about this, but one of you mentioned fires and hurricanes. Does the route we plan on taking, take us through the so-called Tornado Alley?

Thanks again for all the great answers.