The thrift shops were a total bust. The first one had some speakers and an 8-track player. The others had dvd players, but nothing I needed. I went home and did more research. My goal in all of this was to try and keep the spirit of what Monaco had installed, but with some modernity added, so I present you the RCA RT2781HB. I bought ours new in the box from Mercari, $185 shipped. Since I won't be using the speakers that are in the box, I'll just resell them on eBay.
The great part about this unit is that it has Bluetooth, so we can stream from our iPhones (or Android, if that's what you have), and it has 3 HDMI inputs, so I can now connect our Dish satellite box and a BluRay player, and it has an HDMI output to go to the TV. The best part is that the original speaker wires will plug right in and work, as if Monaco had installed it themselves, so it won't look out of place, goal accomplished.
I hope the mods can add this somewhere for those owners who want to upgrade their systems and keep the existing speakers and subwoofer. Keep in mind this is for the Monaco coaches that were built with RCA. I know there were coaches built with Sony.
I'll update, after I receive and install the unit.