A few years ago I bought a rear hatch lock extension bar.  It came in a bag
with text in German so I didn't know that it wasn't recommended for use
when driving (making it of very limited usefulness if you have the rear
screen).  With the extension bar in place while driving with the windows
open, the air flow through the van was smooth and laminar, far superior to
the buffeting we get normally. It made driving in in a Georgia summer
without AC bearable.  I confess that I have occasionally used it while
driving since discovering that it is not recommended, but exhaust gases
sometimes leak in.  I would like to come up with a way to achieve this air
flow without the complication of carbon monoxide poisoning.   Has anyone
come up with a modification that did this?