I'm no 'tight-wad'...but don't see the point of trying to fix this by covering ALL the whys and maybes..I reckon there's a simple-ish answer to keeping the damp air away..
I should mention that my 9m feather-edge timber side gets water-logged during long periods of rain....maybe a smart starting point would be to prevent this with a treatment or lining.....I toyed with that idea last winter but someone that knows 'building' better than I said it wouldn't make any difference...
PD