Giles sorry to hear about the fire, unless you wanted a repaint 
A suggestion to not open hood if you suspect a leaky gas and fire problem. The advise if you do is to have a extinguisher or a smothering blanket.
Having reorganized the CAT pages I like the idea of a fuel shut off kill switch to be turned off prior to parking or stopping.
I do disagree that the stock AC housing allows vapor to coalesce in it’s flat surface. I would also suspect that you may get a dribble or or weeping from non alcohol weeping accelerator pumps and worn throttle plates.
The more fuel in engine compartment the worse things can be . Stock looking plastic filters or a filter in the engine compartment will probably always give up its contents to a boil off mine sure does, but I live with it for now.