My fathers Allegro had the same issue. We found the fresh air intake did not close all of the way when you shut it off. Do not know if it is designed that way.
In his unit it was just over the generator on the passengers side if I remember correctly. I do not remember if he added 7/16 inch thick weather stripping or 'adjusted' the door. The cable actuator would not pull it closed enough.
2017 F350 Lariat Diesel Dually, White, Hitch Kit.
2013 Dutchman Voltage 3200 Epic II 5th wheel.