Troopers can pull you over if they want I guess but if they don't have probable cause, you should be able to get it thrown out.
I don't believe checking a guys papers is probable cause.
There is a huge distinction between commercial plates and a Montana plate.
Being that it is a private coach and not a commercial transport would be just one thing.
I would speak with the Montana Attorney the LLC is with and maybe send a letter to law inforcement in that state. Where's the pushback on this?