also, why don't you try VNC. Seriously, VNC will do what you want. Your computer iwll be considered a remote terminal, as it doesn't have a display or keyboard. as long as its on, use wifi to connect. you might want to consider adding a router to your car. Gigabyte had a small PCI one. i have it and it works great and is really low power. Besides, you dont' need loads of power anyways, as it will be in car. have your linux terminal have a static ip addy, then VNC away to that ip.
If you do all your set up at home wiht a display, and make sure linux boots EVERY TIME without a display, this will work. Plus its free!*
*plus the cost of hardware
I would probably get a SDC so you don't drain your battery too much if you plan to run the computer after the car is off.
-your friendly neighborhood Aximsite/Mobilitysite staff reviewer