I mounted a three outlet 12v plug block on the right hand end of the sink cabinet.  (behind the driver's seat)  I got power from the two fuse block that is mounted at the rear edge of the driver's door jamb.  I have since added a "house" battery behind the drivers seat and put an inverter beside the 12v outlets.  
This location is easy to use from the passenger's seat and from the camper area.  The location is close enough for cell phones or other devices that may be used while underway.
George,
'85 Westfalia