I don't remember the brand but I saw a video of a TT built with the tanks and water lines ALL inside the vehicle, where everything is heated from the furnace interior heat. Hopefully someone will know the mfg.
Some like,
Arctic Fox/Nash , Lance or
Outdoors rv Creekside series . However, i would not use a floorplan with a slideout . I found it to be cold and had to clear off snow and ice off the slide top before i could close it.
Whatever floorplan works for you, can probably be made to work better in the cold by making a few easy mods.
I used foam pipe insulation to wrap water lines that touched outside walls.
I placed 24x24" foam tiles on the floor to make the floor warmer.
I made storm windows as well.
thread on insulation with pics