I'd just buy a cigarette lighter adapter, tape deck / FM transmitter, mini to RCA's, and shove it between the seat and the armrest. And you can probably fit all that stuff in a Pelican case.

Where would the "car kit" go such that you would see the display? It doesn't really make any sense to me. The only benefit I could see is that the FM radio transmitter would run off the cigarette lighter, but they already have one's that do that. A lot of FM transmitters are notorious for interference when you get near powerful radio stations, too.