I have an exit vent in the lower aft area of the fuselage of both my
'27 and '28. With all the other stuff done sealing rudder hinge,
elevator drive, horn splitters, etc, it improved negative pressure and
flow and resulted in less noise. This vent is a huge ass ache to put
in with the associated nozzle, has significant structural implications
requiring reinforcement, and simply, is not for the faint hearted.
The new vent on top is in a low pressure area which helps a lot with
getting flow and reduced cockpit pressure. It also takes an hour and a
half to install instead of about 10 hr. It's structural implications
are minimal. It slightly reduces available baggage storage in the top
center 4 inches.
Both my gliders will have rear vents closed this winter and '28 will
get top vent.
FWIW
UH

What work needs to be done to fit these to other types? Reglass the
cockpit scoop to fit the inside of the fuselage shell?

2C