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They also had a gasoline fired heater, a miniature furnace, as an option. No idea how well it worked, but I can't believe they would even think of selling it today with liability concerns.
I had one in a bus. It was great. You're right it was a small furnace complete with safety devices. Used about a pint/hour running full bore. It was also thermostatically controlled. Safe as propane, maybe safer. The Thing used these torpedo shaped heaters as well as camper busses. The Type IV had a lousy black box gas heater that was more trouble than it was worth.
To answer your question, melt your socks in the front seat, rear seat still froze. When firing up, they sometimes puked fireballs out the heater exhaust above/in drivers front wheel well. They were the upgrade to the exhaust heat-muff heater (any winter Cessna 150/172 pilots here?).
About to say the same thing - a coffee maker in a car that didn't have a heater? I remember the exhaust thing that never worked. But hey, the A/C worked, well mostly. It was the 2/40 model. You know, 2 windows down, 40 miles per hour. Of course it had the patented push start option where you and a friend get it rolling, jump in, drop it in 2nd and pop the clutch. Cause apparently the electric starter didn't always work.
My '59 VWs (and my '60) didn't even come with a gas gauge. If a coffee maker was an option maybe a gas gauge was too?
In 1939, some models also came equipped with showers.What, too soon...?