I bought a couple of these for $5
each:  http://www.mpja.com/prodinfo.asp?number=17384+LA

My plan is to enclose them in something small and opaque and stick
them to the inside of the back window glass in either the upper or
lower corners.  I sometimes carry bikes on the back of my van and
they further obscure the already dim lights.  So these would be
higher and brighter and very visible, and probably illegal on a
technicality.  They only have 2 brightnesses where the vanagon has
separate tail/brake/turn lights.  I have a "hoppy" converter so I can
connect a standard 4 wire trailer connector to the van, so that makes
the conversion for me.  The problem I've seen so far with these
lights is that there is not much difference between the 2
brightnesses.  It seems like they worked per the description when I
first got them, with only 6 of the bulbs lighting on one circuit and
all 12 on the other.  Now it seems they all light on both circuits,
just at different intensities.  I'll post more if I have success on
this project.

Edward