Re: New member, first question!
A few options....
Use silicone or something similar to adhear the plate to the frame
Use small zip ties to hold the bottom of the plate to the frame
Some foam tape (think weatherstriping) behind the plate as well
Or...you can drill the bottom holes and get the square plastic inserts from an auto parts store.
2015 Billet Silver
2012 300SRT, 2009 Jeep SRT, 2006 Charger SRT
Too many mods to list for each, so let's just say a lot was done over the years.