stick with the surepower 120 or 95 amp variety. It is made specificially
for the vw. I think mine is the 95R (R for regulator, which is internal in
your alternator).  go to harold and nancy's web page for details (search
on google for "harold and nancy vanagon" and you'll be sure to find it).
They have very very very clear details and description about how to
install one, etc.

cheers
matthew
ps, i i ordered my battery isolator at the local flaps for like 40$.

Matthew Pollard          "Racing with the wind and flirting with death
Dept. Of Chemistry        So have a cup of coffee and catch your breath"
University of Idaho
www.uidaho.edu/~poll7356