On my last RV7 which also had aluminum vent, the air would force the vent slightly open and cold air would leak. I cut a 1? round piece of foam which fit snugly in there and would keep the gate closed and no air leaked. I can?t remember how I cut it, perhaps with the round hole saw running counter clockwise. It would perfectly and it looked attractive. The nice thing was that I could easily remove it if I needed a bit of air in.