What about an
Espar heater that runs from vehicle fuel? Lots more efficient than idling the engine. Ready secondary fuel source from propane. Can also function as a block heater in some models.
I think these are what the ice road truckers use to conserve fuel and/or have extra heat in similar conditions. Basically any technology used in trucks going to the North Slope is worth considering IMO since the functional and non-functional requirements are similar to PTs use cases.
You don't see those guys fussing with a genset below -20.
Jim