Check out this thread, one of many on upgrading the audio:
http://www.airforums.com/forums/f450...de-161787.html
And yes, what JC puts in these trailers is, shall we say, barely adequate, poorly installed, completely unbalanced, and, I could go on, but you get the idea. Anyone who takes this stuff seriously replaces these systems first thing.
Search the forum for A/V, or audio or video and you will find tons of threads, many with pics from those who have already done it.