[masraum]

Originally Posted by 1990C4S

I would do something with trim that makes a seal, maybe mdf wall paneling/wainscotting? Make them open into the room and the trim plus a magnet hold them closed.

I would also consider making the door a crawl entry, not walk in. Easier to hide.

You don't want hot air coming in.

The holes are already there, some are bigger, some are smaller depending upon location.Opening into the room is the easiest for sure, and probably the easiest to do, seal, and insulate.