The clamps are definitely a good idea. I don't know if the one for the bonnet could be used to clamp onto the side of the car aswell, but you could either put the camera inside the car, depending on how big it is. Or you could clamp it onto the door frame with the window wound down. When it is on the right door frame get the actor on the left to move his/her seat slightly forward so you can see some of their face and do the same when shooting from the left side for the actor on the right. Shooting it 3 times is the way I would do it as you don't want to see a camera sitting on the dash when you are recording your wide master shot.

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