I found out a long time ago to always have the wing vented so that no one area can build up pressure for any reason. When I build a wing, I always have a fair sized hole in each rib (often used to route aileron cables) as well as a vent between the spar webbing and the forward area of the wing. If not, even the heat of the covering iron can cause enough expansion in any cavity to force the covering to separate from the rib/spar surface.