has a bunch of info on Stereo Trailers.
Search for "Stereo" OR "Trailer" to check it all out.
Being the home of RAGBRAI (450+ miles of party biking) This year was the first year I went with a solar panel to charge my batteries.
We have built 15+ trailer/ racks set-ups of all sizes in the past two years. We have spent waaay too much money testing out new speakers, amps etc.
We only use a Pioneer (bullet-proof) TS-TRX40 speaker, and a small 100 watt (cheap) amp, and a small gel celled 12 Volt battery (6-12 amp hours). Get some RCA jack with a male stereo headphone jack, and wa-la plug in any walkman, CD player, MP3, etc.
Depending on the system you want and how far you are willing to carry the darned thing, you can use 1-3 speakers, up to a 250 watt amp and a 12 amp hour battery.
We build the systems more for longevity that bone crushing power. They are loud enough to lead a draft line 20+ long and for every one to hear it, PLUS the system will last 6-12 hours depending on your set-up
The last couple of years, I have foregone the trailer set up and went with a rack setup... Less weight and friction on the ground with the trailer.
Anyways... Look through the RAGBRAI Galleries too for the "follies"!