When I had a travel trailer years ago, I removed the roof vents and installed two Fan-Tastic ventsthat closed automatically in the rain. Great idea! I just went out in a downpour to close the sunroof/moonroof in my Fit. I never open it all the way - just the flip-up at the back. I never remember to close it, though.

Now we're getting thunder and lightning.

EDIT: Rain Sensor Kit
http://www.sportsimportsltd.com/aurasewiwico.html