I'm interested in the subject as well, so please don't sneak the answer
back to Fred via direct email.  

Unlike American vans with longitudinal ridges in the roof, Vgons can take
aftermarket sunroofs in several different spots.  I've mine over the 2nd
seat floor area, where a 6'1" driver can just reach the handle without
driving into a bridge abutment.  It makes a big difference in airflow,
so a sunroof over the 3rd seat or engine deck would probably be an alterna-
tive to the vents Fred mentions.

Some of the VW AC systems make a sunroof anywhere on the roof impossible,
I know.  Fred, is yours the upfront kind or the backtofront kind?
B.
Wm Kennedy
kennedy@admin.njit.edu