I don't, but it shouldn't be too hard to put one in the car... either get one pre-made or do one yourself. They make a variety of USB and serial port LCD displays and there are Linux drivers for 'em. A remote keypad to choose your song... and BAM!
Or just use a small touchscreen LCD.
Either way... the pre-made ones will have shock absorbing mounts for the hard drive. I'd suggest the same if you wanted to build your own.
Me? I just cheat... when on a long trip, I set up a playlist of MP3 files on my laptop, plug in a USB FM transmitter, and it's one big jam fest. I already have the 110v inverter and the laptop for work. It was only $20 at Fry's for the USB transmitter. It also fits a TCB budget.
RJ