Did you stick your head underneath to see if it was a second fuel fill or, perhaps, a different fuel (ie. propane fil)l.  

I’ve encountered vehicles in Europe set-up with propane tanks in the spare tyre tray, but the fill was typically routed to the driver’s side in the same position as the passenger side fill.

> On 01-May-2017, at 14:33, George Gaudette <gcgaudette@GMAIL.COM> wrote:
> 
> Hello folks,
> 
> I'm curious what's up with this... appears to be a second fuel fill
> location.
> 
> https://drive.google.com/file/d/0B8tMxwv9EpaWYUY4ODFTTHJ2WEE/
> view?usp=sharing
> 
> Judging by the screw/bolt heads it looks to me like a custom job. Yes?
> Wondering where the tank is!
> 
> Spotted in Brookline (Village), MA -- hello to the owner if you're reading!
> 
> -George
> '90 Westfalia Automatic
> Brookline, MA