We have a door from the utility room built in the back of the garage into the garage itself. At the bottom there's a quarter inch gap between door and floor. The previous owners added a brush strip on the inside, but wind whistles through.   What's the most effective way to improve the airtightness?   To complicate matters (maybe) the floor isn't level under the door, as the tiles stop halfway under it and a wooden panel continues beyond, a tile thickness lower.