I think you will find that TX, FL and SD are the states most full-timers declare for their domiciles largely because they have no state income tax and are full-timer friendly with numerous mail forwarding services, etc. There is really no reason why you have to purchase your RV in those states since you can have it titled in any state regardless of where you buy. Even if the dealer you buy from is not set up to obtain plates from, say, SD, it is no big deal to get one of the SD mail forwarding services to help assist in that process.
Since you are coming to the mainland without any fixed domicile, you might want to consider purchasing your RV through a Montana LLC. Montana has no vehicle titling tax so your purchase will be less expensive. Setting up an LLC for this purpose is something done by a variety of firms in the state.
I'm sure my comments will provoke reactions from people who will claim this is a scam and you can get in trouble doing it. The people who get in trouble are folks who use this process to try to avoid taxes in their home states and keep the RV in those home states despite registering it in MT. In your case it is unlikely you will have the RV in Hawaii :B so you shouldn't have any problems with that state. There is nothing that prevents people from having vehicles registered in multiple states and living in only one of them; just ask Mitt Romney. You are the perfect candidates for doing this; PM me if you have specific questions on this or full-timing in general.
