Another alternative is to form an LLC in MT, purchase vehicles in MT, pay zero sales tax, title and plate them in MT through the LLC and drive/live where ever you wish. It is easy to do...but it must be done correctly as some unfortunate souls in Colorado learned the hard way.
A nifty advantage to MT is vehicles older than 11yrs get permanent plates. No more fees or effort again as long as you own it and keep up the LLC. RV's, some trailers and ATV's get perm plates right out of the box. Go to the MT website to learn more.
An LLC will cost ~$500+/- to form and there is an annual registered agent fee of $50 to $100. Annual reports are required, but are simple boilerplate if the LLC is just a holding company for assets. No taxes would be due as no income would be generated. One downside is that whatever addy you use in filling out the LLC paperwork is public domain. There are legal ways around that, but it's more $$.
Depending on age, number of vehicles and type, the LLC costs can be easily covered as opposed to paying sales tax.
YMMV