Concertone is about the only RV entertainment manufacturer, that uses systems with this configuration sizing.
many replace it with a Jensen model but they don't make one to fit the hole sizing of your Concertone unit.
some put a different piece of veneer in and just install a Jensen unit.
here's a link to the Concertone product gallery, where you can download a manual for yours:
and Zoe the Wonder Dog(R.I.P.)
'07 Roo 23SS pushing an '07 Chevy Avalanche
Equalizer WDH and Prodigy BC