Camera Setup
I use an Insta360 ONE RS 360 mounted on to the 3m invisible selfie stick. This is secured to the car using a small rig clamp and 2 suction cups from Hague. This setup minimises the footprint on the back window and minimal video editing (if any). Extending the pole too far can give camera shake so its a trial and error based on the road surface and speed..
I also use the suction mounts on all of the panels (roof, wings, doors etc) as long as it is flat and clean to get the multi angle shots.
The RODE Wireless II GO
The Master receiver sits onto of the camera and talks wirelessly to the slave shotgun mic. I tried with and without the muffler - you definitely need the muffler!
Mounted on the car
Both the RODE and shotgun are mounted to a flat surface of the car close to the exhaust. They are mounted using GoPro mounts that I had kicking around, so I can pop them on and off when required.
Location
I found a flat section on the underside of the rear valance to mount the GoPro mounts that I can leave on the car. I have also tried another mic by the intake box by the front arch, no pictures of that as yet.