Could you lay a better camera on a flatbed car and push that car from behind with an engine? So it would be an engineer's eye view. And get power from the rails or from batteries on another flatcar.
It still needs to be quite small, as there are realistically proportioned tunnels, railroad station halls, and trackside buildings a large camera will bump into.
I wind up with about 20mm vertically and 30mm horizontally to work with when you count the space used by the flatbed.
