River Float Boombox Advice

I'm going on a river float trip soon and looking to build a small (Maybe 13x6x6) boombox that will fit on top of a cooler. My main thing is that this has to be basically disposable, so I am trying to avoid scuttling $50. I have some 3/16 plexiglass that a friend at a sign shop was kind enough to donate. I have also pulled 4 2.5" 4ohm altec lansing drivers out of some old computer speakers. (they also say "A4549" and "001027" on the back). I have a cheap TA2024 amp on order:
Mini MKLL TA2024 Tested PCB Power Digital Audio Amp Amplifier Board 12V 2X15W | eBay
I was thinking of a boominator style rig where your electronics are housed in the center of the rectangular box then running each channel to 2 speakers (back to back) in series. For my power source, I have a 12v "4,800" mAh CCTV battery. I have a waterproof case for my cheap mp3 player. I plan to just spray scotch guard or something on the speakers and silicone around the inside seal.

I am not sure about the volume for the speakers as I can't find any info on the drivers. Also, I need to come up with a way to protect the battery and amp while still having access to the battery's power switch (the amp has no switch or volume/tone controls, so I figure I could seal it up in a project box or something.

Any suggestions or advice would be welcome.