I did from the Deep South(east coast, Horse Pens etc) all the way to L.A via Hueco, New Mexico, Arizona, Nevada etc etc. We travelled with a couple who both had vans so that part was easy! What I would say is that getting a good van is actually not that hard, most in America do upwards of 250,000 miles easy cos of the dry conditions and also the cost of new vehicles being low! However getting ripped off as in all countrys is the risk.
The probs are getting insurance, very difficult for a non resident! Most people I met did it through friends that lived there! Also petrol not as cheap as it once was! Saying that it was a great 3 months although trying to eat whilst on the road and avoiding junk food is impossible