30 / 60 FPS dont really give any tangible difference in relation to image quality / plate capture, sure the one lock your lower limit to a 2 X faster 1:60 second, but when you are down there i dont feel like it matter.
I have years ago tried to run 2 identical cameras side by side, and one on each frame rate, and the times the 60 FPS camera got a capture the 30 FPS one did not was extremely marginal. So since then i have never thought about running a camera with 60 FPS.
My small, almost micro JAP 5 door hatchback, well i really wanted to, but something just will not allow me from going above the headliner, well aside for completely taking it down, which i cant be bothered with as the small car allow me to route along the floor if it have to be that way.
You can also some times go along the side up high, and then in between the door / doors rubber weather seal and the car body, but passing by the B pillar you do have to have the curtain airbags in mind at least if it is 2 part and the rear one are tethered to the B pillar like curtain airbags, well at least in my small car are to the A pillar.
BUT ! TBH i dont think there are 2 part curtain airbags, i think it will be one big one covering all the seats there might be in a car.