You can't beat a propex or Carver P4 for out-of-sight installation. 
However, one of the best values in heaters for VW campers is the Platinum
Cat from Thermal Systems in Tumwater, WA.  A photo and description of how I
installed one is on my web page-
http://www.geocities.com/Yosemite/Gorge/1706/vw.html.

Cost is about $330 for the 6000-btu size.  It warms the camper in the
coldest of weather and is not quite as noisy as the propex.  It can be
installed in a box behind the passenger seat and still allows the passenger
seat to be turned almost all the way around.  

Bill