You shouldn't have any problems even in Missoula. I live 50 miles north and travel to Missoula often (I drive Kalispell twice a week). Several people (unicorns?) carry in Missoula that are not part of OCDO. Yes Missoula is one of the most liberal spots in the state, but it's still less liberal than you would think from what you read, just a couple folks that like to push agendas. I have never had an issue with LEO in Montana.
Look out for restaurant/bar carry. You are not allowed by law to carry CONCEALED in a building/room that serves alcohol, this would include places like Applebee's. You must openly carry.
Regarding park carry, I have yet found a city to implement the restriction, not even Missoula. But don't rely on my Intel, check your stuff first. :-)
While your in town, you might as well check out the national bison range. It's not far up the road from me.
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