Here are some pics of a Euro Westy with the propane tank located inside the
van.  This is a fairly common install in Europe.

http://www.autostadtwest.com/images/propane-1.jpg

http://www.autostadtwest.com/images/propane-2.jpg

http://www.autostadtwest.com/images/propane-3.jpg

This is a factory Westfalia install.

Sometimes the vent is located on the driver's side of the van.

Cheers,

Jeff