I'd go with laptops. TuffBooks for starters are designed for harsh operating environments and are probably tops when it comes to resisting damage caused by excessive vibration/impacts. From there I'd mount the laptops on anti-shock plates. A good home-made solution is to place a metal plate on top of a sealed bag of motor oil. The oil in the bag dampens vibration. The metal plate on top will sway/wave rather than vibrate.

I use an older Dell laptop as the "brains" of the DashPC/sound system in my Mits 3000GT and the suspension on it is pretty tight. Haven't had a problem with the computer so far.

So again, I'd definitely go with some laptops for your on-boards.