I have a thermometer that has a wireless sensor about the size of a remote control.  It's been measuring the temp in my glove compartment for a year.  This thread got me thinking.  If you open the driver's side door there is a passageway that was designed to move fresh air to the rear cabin.  Since this area is unused in a Westfalia, it seems like a perfect place to locate the sensor.  As soon as I get some double sided tape, I'll be mounting the sensor in the door.

  Clint