I am not going to participate in the name-calling, but I will state this:
I am quite certain that a small diesel-fired Espar (or equivalent) hydronic unit used to heat a few gallons of water that share a well-insulated box with a set of lithium batteries could run unattended with a high level of reliability for many weeks. Properly designed, such a system would have a level of reliability comparable to any other fuel-driven furnace, including that in a heated garage. The goal would be to maintain a tiny space at barely above freezing, which is a far cry from heating an entire van to shirtsleeve temperatures. The duty cycle (and thus fuel and power consumption) would be quite low, even in winter Minnesota. Systems like this are totally routine in remote telecommunications installations. There is zero reason to doubt that it could be easily done in a van.
I would never want to own a van that I couldn't winter-store without power. I apologize that I am too slow to understand why this is misguided.