I built a plywood box, similar to a guitar amp, covered it in black carpet, installed a JVC am/fm CD player, 2 speakers and an antenna. Mounted a handle on top which actually came from a small guitar amp, wired it all to a trailer plug. It fits nicely between the rollbar uprights and plugs into the other end of the trailer plug which is wired to 12 volts. It has a remote control which works great and is needed as the unit is behind the seats. When I park it can be removed and stored in the trunk, rarely take it out though as I have 2 bicycle locks, the cable type securing it to the roll bar. Sound is great and plenty loud enough even at highway speed. Keeps the car original and is considered portable.
When removed the car side trailer plug just hides under the rear deck carpet.
I'll add some pics if anyone is interested.