Integralle,
As I ride year round I need to be sure my but stays as dry as possible. I used the four bolts that hold the fender on, under the seat. I cut a piece of aluminum that sandwiches a cut up piece of rubber. (old car floor mat). I then screwed the back of the rubber to the plastic inner fender at all four points.
An added advantage is I now have a picture of Marvin the martian under my seat!
I can't see getting any more wet than with a fender as the license plate should deflect the water down. Could be wrong I will let ya know after the next downpour