We found a computer sound system with a woofer and two small speakers that used a 12 volt supply. We plug in a MP3 player that has 5 or six days of music on it and power it with a 12 volt cigarette lighter adaptor when it starts to die, evey ten hours or so.
I don't think my wife will allow me to use it out side the trailer, it might be wrecking other peoples enjoyment of nature. It furnishes backgroud music when I'm cooking or if it's a long rainy day.
We have iphones and ipods but this is a 29$ speaker and 30$ mp3 player so it can stay in the trailer cupboard all the time.
It has a radio tuner but I havent really used it.
It's low budget but it sounds really good so I've never been motivated to upgrade.