If you go to the junk yard, try to find a 76 I think or maybe 77-80 chevy or gmc truck with door panels, the high trim door panels have a piece brushed aluminum in them. They are easy to get out and are big enough you should be able to make 2 plates with 1 panel. Then you get a factory piece, made from factory part that looks like it might belong around the radio.
Just an idea, and it's flat, not bumpy like diamond plate so it should sit flat.