Red/white are L/R audio
Yellow is composite video
Here is how my 2008 was setup....
One set of red/white/yellow goes to the television so you can output DVD audio and video to the screen (assuming your 2005 has a DVD player capability built in).
There is a second red/white pair that also goes to the television so you can receive audio from the tv and play over the stereo speakers.
There is a third red/white pair that go to the subwoofer.
Mine trailer had yet another pair of red/white audio input cables that ran to an aux input in the overhead bin (the idea was that you could hookup your Walkman and play a Cassette over the Streep
If you call airstream they will email you (PDF) the AV wiring diagrams for your particular trailer and you can trace all the wires....