Here are some still pictures
from my BoxCar Cam experiment.
I had to cut a slot in the floor of this tall box car so the battery compartment would fit.
One could make or buy a different configuration that would fit in better. It has a circuit board between the main circiut board and the batteries. The batteries only lasts about 4 hours so you want it to be easy to swap the batteries, or use some sort of manipulated track power. Maybe one of our EEs can help me with that one.
The battery compartment extends below the floor.