There is no best 5th wheel trailer....nor a best brand.
Sounds like your going to need a real/full 4 season trailer. I would concentrate on the 4 season units such as higher R value in the floors/walls/roof in the floorplan you like. This type of input requires lots of leg work on your part digging out the mfg specs on their cold weather pack or "arctic pack"/etc.
With the 2500 Ram your limited to wet pin weight around 2600-2800 lbs plus other stuff in the bed and in the cab before exceeding a its 6000-6500 ? rawr numbers. Over loaded above rawr means wheels/tires/rear suspension will have to be upgraded.
You can get better/more input if you give us the trailer GVWR. WE can't tell anything about weights with a model number or a length.
edit; I did a quick search on the Montana high country 29 RL....it has a 14300 lb gvwr which puts it in a one ton srw truck territory.
