I'm not as 'up' on Mt. law as i am on Wa. law, but here are the points I AM aware that you are mistaken on:
Cities and towns require no permit or license to OC in...Only for CC within incorporated city limits do you need 'permission'.
Banks and places that serve alc. you are REQUIRED to open carry...No CC allowed even if you have a permit.
Courthouse carry is left up to the county level legislature, fed bldg are no go at the fed law level, and I'm not sure how schools are treated in MT.
Dunno for sure about fairs and rodeos (rodeos generally being private affairs, not gummint funded) but BLM, National Parks and Forests are good to go...no permission required.
OC for sure in a car, not CERTAIN about CC but my gut says 'yes' to that as well.