Headface….to answer your question what do the folks living in the million dollar motorhomes do….
First off these people hardly ever stay in an area where its very cold , they migrate to warmer climes .
The folks who live fulltime in their big 5th Wheel trailers and monster RV’s who think they might stay in an area for the winter …tend to go for Heated & insulated Bays where their Holding and water tanks are usually kept from freezing.
They run duct work off their 12-volt LP forced air gas furnaces for this.
Unfortunately School buses don’t have very much room underneath them for building in realistic insulated bays…. Realistic is the key word there. Anyone who hasn’t lived fulltime in a Bus in a very cold place like Alaska or Minnesota just doesn’t get , how fast a tank will freeze after a few days of 30 below temps.
So…In our last bus Home I located the tanks under our bed where they were mostly kept from freezing. The ‘natural Flow of air ‘certainly does not keep the tanks from freezing in a very cold place so we used a couple of 12-volt fans to force heated air under our bed.
Even so , when it got down to 20-30 below and stayed that way we had ice chunks floating around in the tanks.
If I was to do another Bus conversion …instead of locating the tanks ‘As is’ under our bed . I’d cut out a section on the side of the bus. Like I did for the steel boxes I installed in our latest Bus.
And build in a seriously well-insulated box to hold the tanks . I’d heat in with a combination of forced air off our woodstove and a 12-volt holding tank heating pad.
Here’s the link to the folks who make them.
They cost around $120.00