I'm creating plans to convert a Nissan NV2500/3500 into a camper van and that hopefully includes adding an air top heater (Espar/Webasto) in the living area.  These are run on 12V power and efficiently use either gasoline or diesel to burn the fuel in a combustion chamber and then blow the hot air into the space.  I'd rather not have a separate fuel tank for the heater.   So, I checked with a nearby Nissan dealership service center to see if there was an existing auxiliary fuel port on