Doug, I think that on a cool morning you will need fresh air through your windshield defogger system to keep the windows clear. My wife had me modify her car to block off the fresh air and recirculate inside air because of her alergy to the neighborhood insecticides and fertilizers. Sometimes it is hard to keep the windshield clear. If your heater/AC can draw in fresh air that will probably do the job.
I got replacement rubber for the vent doors at Classic parts of America many years ago when they were chevy duty, they probably still have them.
