A true 200 amp alternator is quite large, and needs to be to dissipate heat.
 I totally agree with what Dennis said about Vanagon wiring.  It is totally
undersized for anything other than a nearly stock Westy, and that was when
it was new. I wouldn't add any large load items without rewiring the power
supply side of the van, unless you are into electrical fires. The stock van
charging wiring from the alternator is a single 10 gauge wire.  I wouldn't
want to put a whole bunch of current through it on a regular basis. Charging
a dual battery system from a high output alternator through this single wire
is asking for trouble.

John