mallard, I'll have to send you the design on mine. Me and gandergrinder made the exact same setup last spring, only difference is I went with the 30W speakers for volume, he went with 125 speakers for quality/bass (bass makes for killer murmers that can't be duplicated with most ecallers). We have the same decks with built in amps with 4 channels.
Basically, we took a standard black toolbox. Built a "lift" on one side where the CD player goes. The lift keeps the CD player off the bottom in case somehow moisture gets in. We then cut out the front, in front of the CD player and put plexiglass and sealed it up. This allowed us to use remote controls.
We then built a slot to fit a small deep cycle battery. The battery works all day. Finally we drilled small holes, just big enough for the wires to come through and keep the elements out. I used velcro strips to make the connections tight.
And lastly, stapled stubble straps all over the toolbox to conceal.
When the 2 of us have our systems going the volume and quality is unbelievable. I had pics but didn't turn out but I'll try again.