Quite a bit of interesting information on this thread.
My $0.02:
A) Every state will have requirements for which vehicles have to be registered in that state, based on some combination of residency, domicile, time in the state, phase of the moon, something;
B) Every state will, in turn, impose obligations to pay tax on those vehicles either as part of the registration, property tax, fuel tax, "it's here, we'll tax it" or something;
C) Every state will have requirements for establishing an LLC (or any other type of entity, partnership, etc).
D) Every state will in turn have requirements and regulations about what that LLC must undertake to comply with those establishment provisions and "ongoing enterprise" statutes.
E) Every state will have a tax regime that applies (or doesn't) a tax to a domestic (i.e. created in that state) LLC or other non-personal entity;
IF one has a MH or other RV AND one's use of that MH or RV doesn't implicate tax obligations under A and/or B, AND one wants to setup an LLC in a different state in compliance with the requirements of C and D, AND one is willing to comply with the tax regime of that different state (per E), then go for it.
I strongly suspect that many times there is not enough investigation and the people doing the "Montana LLC" thing aren't entirely compliant with the regulations in A & B or with the requirements of C/D/E.
