Phoenix Cruiser and Nexus RV can do custom work. Both can do added insulation, recirculating hot water, and many other things. Plus, their prices, though more expensive than a usual "C", are not unreasonable. Tiger Motorhomes are decent, but are just outrageous pricewise for basically a class "C" on a pickup truck chassis.
Phoenix Cruiser also can do 4x4 Ford upfits, which are quite useful in that terrain, as well as giving a little bit of a better ground clearance.
I would also recommend to have the RV built with the ability to attach skirting. In cold weather, skirting keeps the wind from going underneath, helping with insulation, and provides additional storage space (be wary of critters though.)
