If yours Montana has the hitch, the flag pole hitch should work ok. However, if the receiver is not nice and tight, the pole will sway back and forth in the wind and you may feel and hear the movement inside the camper.
Another alternative that has worked well for many folks are the flag pole holders that are flat on the bottom with a receiver for the pole. The trailer tire is rolled over the flat base and then the pole is stuck into the the vertical upright. However, if that may not be a good choice either if your awning is directly over the tires.
Another option is to have a receiver mounted on the king pin housing (on top) with a flag flying from the front. You won't have anything to interfear.
I use to fly a flag, but have not done so in years. (we simplified totally our yard ornaments by simply getting rid of all that stuff). But, when we did, I made a simple tripod out of old tent poles and used one of those 3x5 foot flags with a pole and used a couple extra old tent poles to extend the flag pole itself farther up. I used simply bungie cords to tie the pole to the top of the tri-pod and drove the bottom into the ground a couple inches. That way, we could put the flag anywhere, on any terrain, and slopes did not matter any more.
You could also use one of those flat holders you drive on under your tow vehicle tires.
I even did this for a while too:
