IF, the situation is as described, the purchaser intends to use the vehicle they are buying to facilitate leaving their current state I would have no issue with them setting up a Montana LLC and avoiding the payment of a substantial amount of sales tax to a state they will no longer live in. Likewise, I don't have a problem with people who use LLCs to register their RVs if those RVs never enter their state of residence, I.E. they live in New York, yet store the RV in Georgia for the Summer and use only in the South during the winter. In those types of situations, the rig never touches New York, so why would New York be entitled to any tax revenue? Montana LLCs are a tool for special circumstances and in my opinion the situation laid out by the OP meets those circumstances.