[thstone]

To clarify, the risk is that water gets into the cabin and under the seats which could damage the immobilizer (which is mounted under the driver's seat). If the immobilizer stops working, the car will not start (the engine won't even turn over) and you'll likely be stranded.

In regards to using a car cover, be sure that your car cover is water proof. Many car covers are not really water proof since often they rely on a chemical treatment to the fabric that will repel water when new but allows water to go thru the fabric once the treatment gets worn/weathered/aged.