I would also add that even when you start truck engine as emergency feature- diesel in negative temperatures will idle not reaching 80F, so not good for heating. I noticed truckers turn their lights on to put some load on the engine and get it warmer, but it all can go down very fast.
Gasoline engines should provide more heat, but I don't have such experience.
So again, IMHO the only thing that would be dependable is gasoline generator kept warm and started early. This way you can put electric heaters for overnight stay and try use propane furnace to get comfortable.
My Honda 3000 EU would run 6- 8 hr powering 3000W of heaters on its tank.
3000W electric heaters kept me semi-comfortable at 17F, so in negative temperatures they will not make camper cozy, but will allow you to stay alive till the morning.
