Do you have a driver's door? I get quite a bit of air through there from passing trucks. I plan to buy some weather stripping to help seal it up. As for under the dash, check at each side where the firewall meets the outter body. I noticed large gaps on mine and stuff those as well. It did help! I also believe the air comes through the AC unit whether you want it or not since it also acts as the defroster. Turn up the heat and send it to the floor. We haven't done this yet but I've read where others have installed a curtain just behind the seats to help block the cold air inside the coach from coming forward. Smaller area, easier to heat!!
2007 Georgetown 370TS
aka - RAYNMKR