here is a photo of a Hostess Tray...not saying to get this...just as a guide to make your own...you can make one out of 1in Speedrail for very little money....
but with that in mind:
The foremost important thing to have is redundent safety features. Or, make sure all the gear is strapped and clamped down tightly. And that includes the talent and crew inside the vehicle. You are going to become a magnet for rubber neckers. You have no control on their driving. So, put a safety strap on the camera to hold it in place. Don't trust just one hard point. Use extreme care when handling the hostess tray and hood mount. These things leave BIG ASS scratches and DEEP gouges if you bump the car. Your key grip and and his/her dept. will need plenty of time to rig. DON'T rush it.
And remember you vehicle is wider on one side than it was before...take care when driving to have extra room on the side of the camera...and you dont need to be moving fast as from that side angle things will look fast anyway.