Very sad. Some things still not clear to me. He was using shore power via extension cords to heat the van electrically while parked in the recycling yard. Then he moved down the street. Did he have shore power there? Was the problem with ac electric, or with the van's dc system? A properly fused dc system should not be able to start a fire - the fuses should blow before the wire gets that hot. With ac, a thin extension cord pulling too much power, could overheat before the circuit breaker blew, especially if it was a 20 amp outlet and nothing else on that circuit was drawing power at the time.
And of course, probably no smoke alarm.
Lessons: Properly thick wires, Right sized fuses on EVERY circuit. And of course, a good smoke alarm.