OK, I'll start. I had an old Plymouth station wagon. When it sat out in the rain, water would somehow get in and collect in the fresh air vent duct under the dash. When I'd make my first right turn, cold water would spill out all over my feet. For the life of me, I couldn't figure out where the water was getting in . . . so I found the lowest point in the plastic duct, threaded in a 90 degree fuel hose fitting, and ran a 1/4" drain hose under the carpet and out through a hole I drilled in the floorboard. Problem "solved." Next.