If it is the problem I have had, then your fuel tank is
corroded through on the top of  the tank, where the large
hose from the auxiliary heater heads forward to the cabin.
If you fill only half full it probably won't leak.

        If you operate the aux heater, the leaked gasoline will
have soaked the large paper/cardboard hose from the output
side of the aux heater, and when the heater starts to put out
heat, you will smell a lot of gasoline inside the van. This is not
a time to light up a cigarette and contemplate where that vapour
came from! ! !

        I took my fuel tank out and put a patch of sheet metal
on top of the corroded part, brazing it in place. Then I used
epoxy paint over that, and then rubberized tar over that. It
has worked perfectly since then .

         My van is diesel, but the symptoms are the same as yours

        It's a real nuisance taking out the tank, but I don't know of
any alternative.  A new tank costs a fortune from VW. Perhaps
you could scare up a used one. Good luck

Gary Meek
Sherwood Park, Alberta, Canada

82 Vanagon TD
83 Quantum TD