I somehow got both the furnace and the refrigerator running — and just in time for heat as the weather turned even colder. I’m still not sure what the problem was — I removed the exhaust system and banged on some things, wiggled some electrical leads, and probably for other reasons, the heating system kicked in and stayed lit — operating normally.
So it’s been comfortable in the Airstream. Last night, as I returned from the house, I found that the lights were dim and the blower was laboring. Dying battery! I guess it’s not surprising given the draw of the blower motor. (I’m planning to have at least one more battery for boondocking — so this confirms that plan.)
It was late so I nosed the truck in toward the trailer, hitched up some jumper cables, and got juice flowing so that the heating system and lights worked.
You can guess the rest of the story: this morning, the truck battery was too low to turn the engine over! Fortunately, a quick jump start from my daughter’s Jetta got the Ford going, and we’ve got the trailer battery on a charger. We’ll be all set and have new impetus to set up a better system for future boondocking.