All I have to say is "application, application, application".  Listen an old
VW mechanic explained it to me this way, he said, "VW stands for Volkswagen
that means "People's Car".  As long as you use them to move people around in
you are OK.  You start using them to tow things and then you are in trouble."
These vans were designed to move people not to tow stuff.  You can put an
incredible amount of weight inside a Vanagon and it will not hurt anything (I
have loaded my '85 Vanagon down with VW parts and taken long trips and the van
actually rides better with the extra weight and I had no problem keeping up
with traffic.
However when you put a trailer behind the van or tow another vehicle you add a
variable that the designers of the Vanagon didn't factor in.  Then your van
becomes a "test vehicle".  If you have a small trailer with only a few hundred
pounds on it, this shouldn't be a problem, but towing another vehicle or
equivilent weight in a trailer is just not a good idea in my book.  You could
be creating a potentially dangerous situation where the van may not be able to
brake properly, or may get rear ended on a mountain pass because you are going
unexpectedly slow.
The waterboxer motor was not made as a tow-truck engine.  It was made to move
people and thier stuff, inside the van (or possibly strapped to the roof).
Of course if you were to upgrade your engine to one that was made to move the
extra weight and that could handle the stress easily because it has more power
and torque, then this would change the picture.  Now your motor fits the
"application" of a tow vehicle and you might just have to upgrade the braking
system a little to achieve a decent tow vehicle (this is what I am pondering
for this summer).
I know I am going to get flames on this one.  Please p-mail only unless you
have something constructive to add to the conversation.
As for me I ride in my '91 Carat Vanagon or '84 GL or Jetta Diesel, and (for
now) I tow with a '86 Dodge Ram Van (Ugh!).  It rides like junk but it was
made to be able to tow.
My 2 cents
Ken Wilford
Van-Again
John 3:16