I've been working on project related to this, but the stereo itself has been the last piece I haven't touched yet as we don't listen to music/tv throughout the trailer that much. What I have done though is taken out the old unit and used a piece of white plexiglass (our trailer is all white inside) that covers the old hole. I added a 12v plug outlet to one corner using the power feed in the old harness. Next steps are a couple of USB charging outlets in the panel and then a speaker selector of some kind. The selector is what is holding it up as I can't find one I like that will work for 3 pairs and that I can integrate into the panel. I might pick up something like this http://amzn.com/B004TBF90C and see if I can hack it apart so that I can just have the 3 switches in my panel with the guts hidden behind. Then the final piece would be a single DIN auto receiver with bluetooth and 3.5 in of which there are plenty.
