I have a few custom vanity plates so I ordered the
Altec Autocross frame to keep it looking new (similar to Weathertech). Chrome or Black Acrylic frame with a clear plastic cover to protect the plate and a rubber gasket that sits flush on the car to keep water / dirt / debris off. I liked the look after install so I got a few of them for my other cars.
http://www.autogeek.net/autcroslenfr.html
http://www.autogeek.net/weatclearlic.html