I sealed all openings with foam under hood. There are quite a few of them. We use a spot light at night to see most of them, others we took a hand full of incense with fans in window sucking air out of RV to see any other ways air was getting in. Then when we are parked we cover the front end so air can not just blow in grill, just have to remember to remove it before driving off.
Bob-Liz Merry Christmas