My personal experiance is that the water was coming in from the wiper cowel on the passenger side. The rain runs down the windshield, goes past the cheep and prob by this point worn out weatherstrip gasket on the plastic cowel cover, runs down past the heater/AC blower motor fan blades, drips onto the passenger side floor, then collects behind the front passenger seat. You can get an updated water deflector from the dealer that sits below the plastic wiper cowel and above the fresh air intake (where a cabin air filter would go if you have done this mod on your GP or own a Monte or Buick since it is stock on most of them). It tucks under the windshield a bit and is much longer that the air intake opening. The GM part # is 12591982 and is labled as a "shield". Mine cost me $9.14 after tax. I had about 3 gallons of water in mine from sitting for a week while it rained everyday. This resulted in pulling the seats and carpet out to allow things to dry. On the flip side I used this time to line my entire floor and interior with Dexdamp sound deadener.Hope this helps.
