Other State Registration

You probably should NOT take your RV home to Idaho!
While the "three state" thing may be illegal, there are a LOT of rental units running up and down the roads in this country that are registered in one state, driven by someone licensed in another state, and operated in a third state, with a rental contract filled out in a fourth state!
Yeah, I know, those are RENTALS, "that's different".

I don't want to be illegal, but I don't want to pay any more in taxes than I have to. People doing what I'm discussing are not doing anything illegal; unethical, maybe. Loopholes exist everywhere, and if it's good enough for John Kerry and his yacht, it's good enough for me.

If you really want to cheat your state out of taxes, why not just go all the way and create a MT LLC? At least that will be sorta legal.

Your best bet right now is to make sure you never get stopped. You're probably more likely to get reported by a neighbor than getting stopped.

I believe you may have a problem if you register in a state other than where you reside and from which you have a drivers license. Used to be and I believe still is if you get stopped by police in one state, are licenced in another, and registered in yet another (three different states) you are illegal. Two of the three must be in one state. I almost ended up in jail late one night. Was licenced in illinois, lived in Colorado, registered in Texas. Was while I was in the service and while I was wrong, it kept me from jail on a Sat night of a three day weekend. Also your state will be missing your taxes and may come after you with penalties and fines if you get caught.