A K&N air filter drops in just like the stock.  You clean and re-oil them
rather than replacing them.  According to their literature they filter much
better than stock paper filters while passing much more air.  Plus they have
a million mile warranty -- I'm looking forward to collecting on that in about
99 years!  A lot of FLAPS (NAPA, Autozone, etc.) are carrying them now but
will likely have to special order one for a Vanagon.  Fast German Auto and
Summit Racing are two mail order sources I know of.

Chuck
Filtercharger equipped '85 Wolfsburg Westy -- 'Roland'