It never hurts to check.
These are works in progress. I do need to deal with air ingress. Two of the designs in
#post343378 address this. In fact you could combine the second of those with the ducted design just above.
I lean toward harvesting the air as it spills over the drip rail and tries to form a vortex.
Have you seen the route air takes in the Type III Notchback?
In just below the backlight as on a Beetle, but then
out to the sides,
back through the fenders (where the Squareback picks it up)
down to a plenum in the rear valance, and then
forward into the engine.
Just today I found this (Wikipedia, I think):
I'm looking at it and thinking about a rear partial belly pan. I have a trailer hitch that reaches from the torsion bar housing to the back bumper, it might make a good foundation. It's certainly heavy enough.