If you are looking for a few pointers as well, I'd try e-mailing the guys at http://www.classicresto.com/. They were the first to drop a mini into a car and I'm sure they would know for sure.

But with the interference, it sounds like you are not getting constant power. You could try dropping a small regulator between the power connection on the display to see if that would help as opposed to possibly killing a mini in the process.
MacBook 2GHz Intel Core 2 Duo w/ 2GB DDR2 RAM & 120GB SATA 5400RPM HDD
Canon Rebel XTI
Google Cr-48 Beta Laptop