Another thing I have done is to spray WD-40 along the seams inside the doors and hood and trunk lid. Usually you can get through a drain hole and let it do its thing. Since WD stands for "water displacement" I figure if it gets into a small gap in a seam where two pieces were crimped together. Cheap, takes only a couple of minutes, and I figure it can't hurt. If moisture is going to get trapped, those are likely places.