Mice can enter the vanagon through the ventilation system.  Remove the
front top plastic grill, and notice the small plastic grill over the air
intake for the ventilation system.  Run your finger aroud the left and
right side and notice that at the top especially there is room for mice,
snakes, etc to get in.  Wasn't that kind of VW to provide shelter for
these unappreciated creatures.
    Seriously, I have had lots of trouble with mice getting into my
Vanagon in the winter, here in Iowa.  They leave a real mess, and
smell.  I have resorted to blocking off the open area with a foaming
type of house caulk/sealant.  Mice could chew through this, but they
don't seem to bother it--I'm glad .
    I would advise everyone to watch out for this problem.  Once a mouse
has lived in your van, the smell is disgusting.  It takes a lot of work
to get rid of it.

Chuck Hill