Our Roadtrek came with the original radio, AM/FM/CD/Cassette. No way to plug in a phone or ipod, so an upgrade was in order. It turns out to be easy to change the radio, just pry off the plastic dash cover, undo 4 bolts, pull out the old radio, and insert the new one. I got all the parts on Amazon:
This one has AUX in, USB, bluetooth, CD, AM/FM, so a little more modern than the OEM radio. Amazon link.
Since it is smaller than the OEM radio, I needed a mounting kit and a wiring adapter: