Questions about whether you need a sliding 5th. wheel...
Quick answer...
... 1. measure the distance from the center of the hole in the 5th. wheel plate (in your pickup) to the back of your truck cab...
... 2. measure the distance from the center of the king pin (on your camper) to the front corner (not the side) of the camper...
... if the distance to the corner on your camper is less than the distance to the cab from the center of the 5th. wheel, you probably do not need a slider.
If it is only a few inches less you may still need a slider cause it might not be totally level when you are turning and that will have an effect on your clearance.
I think the newer Montana's (maybe all?) have an extension on the king pin unit that puts the pin out toward the front edge of the camper.... reducing the clearance needed...
I'm new to this group and I just bought my new 5th. wheel Montana 3400RL, and I have a crew cab chevy that has a slightly shorter bed and mine clears fine (although I did buy a slider just for the possibility of needing it.)
Hope this is helpful.