I think I've seen this type of heater used for extreme camping to heat a tent. It looks like it has a built in tank for kerosene or diesel. Is that about right what I'm thinking of Frank? And the 12v is for a blower motor. A mini furnace, I'm guessing 3KBTU/Hr.
So does this warm the engine compartment by just blowing the hot air.
I grew up in North Dakota, where tank heaters were connected into the coolant lines of a gas engines. And many places had a power source for them. Starting an engine at -45F can be fun. I figured out when Mobil 1 came out that it was worth the $2.90/qt (vs $0.65/qt conventional oil ~1969). As my V8 389 Pontiac would always start. That and use a huge battery meant for a Cadillac.