I had the same issues. I thought I would get something like
this Pinoeer that does exacty what the original RV unit does. Wire the 4 inside speakers to "front" and outside to "rear" and use fader to control inside vs. outside sound. But then I would still have poor speakers. I ended up getting a $50 portable/car DVD player and $60 bluetooth speaker. That offers more flexibility for us, better sound, and lower cost.
A & A parents of DD 2005, DS1 2007, DS2 2009
2011 Suburban 2500 6.0L 3.73 pulling 2011 Heartland North Trail 28BRS
2017 Subaru Outback 3.6R
2x 2023 Chevrolet Bolt EUV (Gray and Black Twins)