This is a very old thread but I thought I would add that I am close to agreeing a deal to buy an RV privately in the USA. The owner is an Aussie and has registered and insured the vehicle in Florida as a foreign resident. You need a US address to do this but they are easily acquired. He does say that his insurance is maybe double what it would be if he had a US drivers license. He also has a bank account, but I will be asking him about this, harder to get than the insurance.
I hope if the deal goes through to register in Arizona, no annual test outside of Phoenix and Tucson and warm enough not to need winterising when away. Regarding the Visa Waiver program we plan to do our Road Trip in 2 month sections, gives us a little spare time for emergencies that may arise.