This is a bit of self promotion, but I built an entirely open-source dash-cam that excels in this scenario. Instead of recording to an SD card inside the camera, the camera is connected to a capture device installed somewhere else in the car.
It's not perfect, but it's very time consuming for a potential adversary to locate the video storage. It was designed like this primarily for car break-ins, but it would work well here as well.
It all runs on a generic Linux SBC, so there's technically nothing stopping you from encrypting the SD card too.