I had the same problem with my '88 Westy. Turned out to be one of the rubber
gaskets of the vent tube that connects one side of the top of the tank to
the other.  I have a photo of the top of the tank (removed) with the
associated pieces that I can post or email to anyone who is interested.
There is also a good photo in the Shop manual.

The way I located the leak was to fill the tank full - then use a flashlight
on the top of the tank to locate the leak. Not a good way if you live near
open flames - however.

Joyce and Bruce wrote:

> Hello Volks,
>
> My '85 Westy has a strong gas odor outside the van after I fill-up.
> It's mostly on the passenger side and goes away after a few days.
>
> No, don't see anything dripping from below but I suspect something is
> wrong. Has anyone else had and solved this problem before? TIA.