>> Hanging 200 pounds behind a Vanagon needs to be done with care. As the
>> load moves further back, the actual load on the rear axle increases and
>> the load on the front axle are lifted.

I recently looked into this again.  My original setup at:
http://www.telusplanet.net/public/gary2a/rack/motorcycle.htm

If I were going to do it again, I would make a dedicated carrier which
replaces the bumper.
I personally do not like the motorcycle carriers which plug into a hitch
receiver, at least not on a vanagon.
http://www.motojackrack.com/

My idea was as follows;
Remove the bumper.  Remove the old bumper mount brackets.  Use new longer
mounting brackets which go 2 1/2 times deeper into the body of the van,
using three bolts each instead of two.  Build a tray carrier upon the TWO
brackets sticking out of the van.
This would be far more stable than a single center mounting point, as with a
hitch carrier.
The downside is that you cannot remove the carrier quickly and you don't
really have a bumper.  There are also valid issues with hanging weight on
the back of the van which is another topic.  But, I would have confidence in
the motorcycle carrier itself, if built that way.
See this page for bumper brackets:
http://www.telusplanet.net/public/gary2a/rack/bumper/bumper.htm

When I last had a motorcycle, I was using a trailer behind the vanagon and
was happy with that.
I think the original poster was looking into carrying a lightweight moped,
which would be easier than a heavy motorcycle.

Gary Lee