Look for RVs labeled "Arctic Ready" or "Four Season" for winterized protection.
Gulf Stream,
North Wood, and
Starcraft, among others, all have RVs with the above designation.
For the OP, who bought a TT without knowing to inspect for use in winter, I'd suggest he could insulate his tanks and enclose with a belly skin. He could also divert one of his furnace ducts into the new enclosed space to heat it. This won't be a perfect solution, no telling about plumbing runs and dump valves, but it's a start.
Water tanks under the bed is a common strategy in Class C and gas Class A RVs, I've seen it in some TT but I can't recall the brands, models, or years they did that. Of course the black and grey tanks are still underneath and insulated, skinned, and heated in a variety of ways.