When I had my windshield replaced a couple of years ago, the guy who was actually very good, asked if I wanted to use seam sealer. He asked if the car would ever see rain or be washed. I said no, so we never put any in. Being here in AZ, we hardly get rain and if it even looks like it is going to rain the car does not come out. I hardly was the car too since I keep it covered in the garage and wipe it down every time I take it out. If I do have to wash it due to thicker dust (from a windy day), I use the shower or mist function on the hose and try to stay away from the windshield as much as possible.