I highly suggest giving her a good run before you load into the car. Bike, fetch, disc, whatever, just tire her out as much as you can before hitting the road.
A tired dog is a dog that's more likely to be accepting of the ride.
Make sure she's got a comfortable place for the ride. Whether it be secured in the seat, or in a crate.
Pack some long lasting treats for throughout the day. Things like kongs stuffed with peanut butter & kibble, then frozen, can work quite well.
I'd suggest making a stop at least every 2-3 hours. From what I've seen, most of the interstates have fairly regular rest stops with some grass for the dogs.
While I can't give specific locations - as I am Canadian and not familiar at all with most of the areas that you'll be driving, here are a few links that I've used when travelling:
http://www.doggoes.com/
http://www.dogpark.com/
I get that dog parks aren't always a favourable option for many. If you catch them at the right times, it could be a good way to get Foxy out for some exercise sans-leash.
Best of luck!
We'd love to see pictures of your travels