BenT and others have mentioned me for the locking gas cap.  I don't stock caps, and generally refer questions to our list suppliers on that item.  Here's what I have found.  The Syncro cap is designed to use the ignition key.  The standard van uses a different key.  The lock in the cap is of very poor quality, however.  Due to being made of plastic, they are generally worn to the point where anything will turn them.  I theorize the gasoline vapors also soften the plastic and aid in it's deterioration.  Once assembled, the caps aren't designed to be taken apart, though they can.  Therre's no reason that, if the ignition key will enter the lock, it can't be keyed to work from the ignition key.  It's not a secure lock, though.  Even correctly keyed, it doesn't take much force to bypass it.  Just my thoughts on it, and it's possible that I'm wrong on there not being a standard Vanagon cap that uses the ignition key....I've just never seen one.
Steve Sandlin