has anyone ever used Rain-X or an equivalent product on the outside of their tank? I'm wondering if it would help minimize the water spots that I seem to be cleaning off every time I turn around. Theoretically it should, as it would cause the water to bead up and off the glass and not dry on the surface, right? I know it works great on my cars...

Thoughts? One concern would be if it has any weird reaction with light to make taking pictures a problem. Although you'd think there would be traces you could see through a windshield in bright daylight or at night against oncoming traffic...