Wouldnt it be better to make a dashcam with an external DVR? That way you would 1, Reduce the camera footprint for a more discrete approach. 2, More easily accessible SD card and DVR + other features. 3, The biggest problem of all, The main electronics will be out of direct sunlight resulting in little to no heat soak.
Having all the electronics in one place especially in such a small camera causes a large amount of heat it's self, throw in direct sunlight and you have a very expensive dummy camera with rapidly degrading electronics and many failed SD cards.
I Personaly think this will be a better option and with the possibility of adding more cameras.