I towed an Iltis (3,000+ lbs.) several times with a high top Westy Syncro
camper.  The only complaint I had was climbing the passes with the stock 2.1
liter motor.  Braking on the down-grades wasn't a problem.  Cruising at
65MPH on I-5 wasn't a problem either.  However, I can see how it would be
hard on a Vanagon with an auto trans.  Other than that, I don't think it
would be a problem at all.

Cheers,

Jeff