When we erected our polytunnel it created a rain forest type of micro climate internally. The water literally dripped off the roof/sides making the aircraft wet and damp for a lot of the time. The plastic was allowing the moisture in the air to condense out when cold and yet not evaporate when warmer.
The solution was to put louvred panels into either end - about 10 sq foot each (just made with pine framing and cladding). The ventilation transformed the dryness of the hangar (tunnel). Of course the heating was made more difficult, when we're working on the aircraft a mobile Super SER gives some warmth but the 'answer' is a gas blower. Neither are cheap in terms of the gas they burn - but then we do not heat for that long.
Best of luck.