What I do:
Mainly, heat the occupants and not the space. I use my heated mattress pad, extra heating pads as needed, and one for the cat, on inverter. And lots of blankets. I do my reading, netsurfing, tv watching in bed.
For getting dressed in the morning, I turn on my 300 watt home depot heater for 2 or 3 minutes, also on inverter.
The cold-night places that I boondock tend to be warm in the daytime. For 24 hour cold, i go where there is electricity.
This may change when I pick up my new giant batteries. I could also see running the propane stove a little, when I get my bigger van.
The hydronic heater looks awesome.