Not to throw yet another aux battery hookup configuration into the pot, but
I expect to have (in about a month) genuine Hella dual battery wiring kits
from Germany.  Just Kampers has been using these in the UK for quite some
time and has been very happy with them.  As I understand it, the kit acts as
an isolator between the two batteries when the van is shut off; when
running, the alternator first charges the starting battery first and then
the aux battery after the starting battery is fully charged.  Wiring the kit
to the alternator takes under an hour and is reasonably simple.  Projected
price is about $60. Stay tuned.

- Ron Salmon
  The Bus Depot, Inc.
  http://www.busdepot.com
  (215) 234-VWVW