While this isn't my area of expertise, I think Bimmer1 is going to luck out because he's in Florida and so is MT.
Therefore, there's no "crossing of interstate commerce lines" involved for the Feds to poke their noses into. The Feds regulate "interstate trade" in switchblades so if he wanted to buy, say, a Benchmade auto from Oregon, he'd be screwed.
If he's 21, he should score a Florida CCW permit because that'll give him unrestricted concealed carry rights on autos, big fixed blade knives or of course, guns, which he may or may not be into.
What I *don't* have any clue on is whether or not he can open-carry the auto without having a CCW permit. Mike or Spark will probably know, or go post on the auto forum.
To all: you can't begin to sort out somebody's situation without looking at their home state.
Last: I AM NOT A LAWYER, consider this a starting point for further research.
Jim