We've never been further east than Phoenix by road trip, but if you have time, you might want to check out Death Valley on your way. It's a great place to visit in the winter. I know of a nice campground there, if you're interested, pm me.
There's also a nice, laid-back campground in Desert Hot Springs that you might like to spend a night or two in, it's called Sam's Family Spa
http://www.samsfamilyspa.com/index.html. The mineral pools are wonderful, it's really quiet, and very reasonable.
We're hoping to go back down there (to both places!) during winter break, weather permitting.