Greetings & Welcome!
As a long time, often extreme weather, full time nomad, I respectfully think you need to re-examine your options…
Plumbing doesn’t work in below freezing weather, and water heaters need to be drained and the plumbing system winterized. Even the tankless water heaters will freeze up & break unless they are fully drained. My solution is no plumbing, and no traditional water heater.
Spring, summer, & fall, solar heated hot water fills most of my needs. If I need more hot water, or during the winter, I can heat water in a pot on my stove, or if I need more hot water than that, I have a fire coil which can be used with my stove, under a pot or frying pan. It is a coil of copper tubing with vinyl hoses attached to the inlet & outlet. You can place both hoses into any water container, and it will continually recirculate hot water through it, getting hotter with time. You can even bring the water to a boil if you leave it on long enough. I store my 2x 7 gallon water jugs inside, and when it’s below freezing I frequently run my heat 24/7, so the water jugs never freeze. Before a shower, I will heat one whole water jug to hot shower temperature in ~ 5 minutes.
Correct me if I’m wrong, but don’t the Webasto heaters require power to run? For many people, power is a huge problem in the winter, when solar panels work poorly, or not at all. I don’t like any of my essentials to require any sort of power, so I use a multi-fuel capable wick type kerosene heater to provide cheap, dry heat. I have a heat powered wood stove type fan that I place on top of it to have fan forced & circulated heat with no power needed.
It is totally possible to live comfortably, and with full amenities in extreme weather, but we need to readjust conventional thinking to accomplish it. As a child, we would tent camp for weeks at a time, without electricity or battery power, and frequently in extreme temps, both hot & cold, yet we always remained comfortable. Newer isn’t always better, and old school cool often offers the answers we need to thrive, not to just barely survive. Did I mention that it’s often cheaper & more reliable too?
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