Based on my experience, a negative pressure inside the cockpit will do the
trick.
This is base on having built two gliders and own an ASW24.
Providing the perimeter fit of the canopy is good, no edges of the
canopy frame are sticking out that is all that would be needed.
Case in point. When I picked up my ASW24 the canopy frame was covered
with foam tape and the front and rear edges were raise. I removed the
material made sure the canopy frame got back it's original fit.
Then I improved the exit ventilation at the tail. The Cockpit is now quite,
plus I stay cooler, due to better ventilation flow
Regards
Udo