Mark,

Stan the wildman from TX installed a PVC pipe as a scoop up front for added
venting. Why not cut a whole in the rear side window glass and do something
similar. Valves for large diameter PVC pipe is available. That way you can
open and close the. If you can't get holes done on glass, get Plexiglas
installed on one side. You can even get creative and put small reverse NACA
ducts so as not to disturb the airflow much and still have an efficient vent.

I tried to modify a stock slider for rear installation but could not get the
corners bent w/o breaking the aluminum. I will try to get some done
professionally at a later date.

BenT
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