Don't get me started on brothers.
I don't know which model Espar Hydronic they're installing. I'll know next week. Looking at the manual, depending on the model and what you have it set at, the Hydronic coolant heater will draw between 2 and 4 amps and will function with the battery down to 10v.
Arctic Fox has a number of items that might be fun/useful. They have both fuel tank and battery heaters that work with coolant heaters like the Hydronic. I bet there'd be more than enough juice in a 4D or dual battery system to start things moving, assuming the diesel hasn't gelled in the fuel line. Once all that starts warming the batteries up you'll will have more power. It says you can get a 7-Day timer as well. If you can have the Hydronic timer turn on one of their 12v heated fuel lines as well then you're all set. With something like the chili dog starting the van once or twice a day you're even better off. Though, ideally, you could have a
CarPC with the proper controller coordinating the whole thing.
Or, if I do ever make the trip, I could just leave the motor running.
I do think it's funny that this would be using the Hydronic for it's intended purpose rather than making hot water for dishes and cocoa.