I use a really thin coat of dope (30-40%) as a sanding aid, to knock the balsa fuzz off. But if I use too much dope, the plastic covering bubbles underneath. Not sure if the covering heat is out gassing the dope or the dope has created a barrier that prevents the air from passing through the balsa. Maybe both.
Out of FF habit, I do dope all the structure (ribs, spars etc.) to minimize humidity changes. Probably totally unproven, but I do it anyway.
Norm