JACKPOT!!!
Wife is sewing new seat cushions for the dining room chairs and I got the old foam. Fit the foam in the roof vent in the bathroom, a piece in the box access door and another in the over the stove vent (fan just pulls off so pulled it off and put a piece in for now).
Am in the middle of designing a sliding door for the vent that will go between the wall and the fan body and I can slide open when I want and closed when I want. Using a piece of scrap plastic and there is already a space there. Will have to see if it works.
When I was working in the TC it was -2 when I started and 20 minutes later it was 18C. Every little thing helps and that is without the storm windows.