I think all the RV audio systems are junk. Every component stinks unless you get into some of the higher end 5er and motorhomes that use home theater style systems. I looked into replacing my poor OEM system with a $250 mobile/car stereo DVD player head unit. That would have done everything the OEM system would do, with better quality and easier use. I was planning to use the fader to control inside vs. outside speakers. But then those speakers all suck so that's another $100/pair for anything decent.
Do you need it to run off 12V power or is 110V AC ok? Some kind of 2.1 or 5.1 HTIB that runs off 110V AC is probably the easiest/cheapest path to good sound with good usability. Most do not have AM/FM receivers, though.
I ended up buying a $60 portable bluetooth speaker. We use it almost every day, home or camping. It sounds far better than the RV system. And we take it inside, outside, the beach, campfire, around the yard, etc. Wish I spent more on an even better one. Another $50 portable DVD player that runs off 12V DC or 110v AV. I run video to the TV in the trailer when inside and audio to that speaker which also has 3.5mm input. Now we stream most media from smartphones/tablets.