Age of fuel lines. Rubber deteriorates over time. Hole in fuel line,
hot engine, add a spark, and boom, engine fire.

Replace fuel lines to correct issue.

Another consideration why Vanagons might be more susceptible than other
vehicles is that the fuel tank is in FRONT of the vehicle and hence as
the vehicle travels down the road, a leak is more likely to come back
towards the engine, than away from the engine.