Craig,
   I would take it to a professional, like a store that only sells batteries
and have the system tested again. I take mine to a local place called
Southern Batteries. They do several tests including a load test, all for
free.
   If not that, at least take it to a FLAPS (friendly local auto parts
store) near you. They can do the same tests but results may vary.
   They were able to diagnose the "low charging voltage with all electrical
consumers on problem" on our 85. To fix I had to clean some grounds and
upgrade the wire between the alternator and starter.
   The weak wire was solved on later Vanagons by VW.
Ken Lewis
http://neksiwel.20m.com/