[s-cars] Gas smell in cabin - where to look?

[Tony Curran]

Was passing a gas station when I first noticed the smell but then it didn't
go away. 
 
No obvious signs of leak. Any primary suspect areas? Looks OK around filter
but that is where the smell is strongest. Unfortunately the lower parts are
wet from road spray so will have to wait till morning to take a closer look.
 
Appreciate any insight.
 
Tony
96 S6 - with the blowin' exhaust and fuel system!