Totally the wrong solution to a rattling license plate man. You dont use deadener for the license plate, complete waste of money, there's way more effective options then using deadener.
Put these to the back and then screw your license plate in tightly top and bottom.
You need to decouple the surfaces meaning dont let the metal to metal surfaces touch each other because they will rattle from the vibrations.
Dynamat sucks @SS if you want good stuff, go second skin damplifier pro. If you want cheaper stuff thats still miles better then dynamat, use stinger road kill or knukonceptz kno knoise. Gotta get out of that mainstream mindset you got there man, get more for your money with better quality products.