Vanagons have two typical areas for fuel leakage that is noticeable inside:

1. Bad fuel tank vent fittings. On top of the tank there are a number (4?)
plastic fittings that are responsible for connecting and collecting the tank to
the system that controls evaporating fuel. Some on the list have been able to
reach them with the tank in the van, I have not.

2. Rust holes on tank top. There is an air duct that is part of the heater
system that snakes around under the van on its trip from the engine to the
cabin. It passes over the fuel tank. Very often sand, salt & dirt collects
between the duct and tank and the heat from the duct all combine to make rust
holes.

If it is number 1 many have "solved" it by not filling the tank "full". Dropping
the tank to fix this is not hard, two straps and the fuel lines/evap hoses/fuel
gage wires are all that it takes. An empty tank helps too.

If it is number 2 then the tank must be removed and repaired or replaced.