I scaled this up from a nicely done Gauge 1 design.
The limitations of my bed meant some parts had to be sliced to print and then joined together afterwards. I chose a 2-3-2 split for the chassis-bed-sides, in an effort to retain some strength upon assembly.
The axles are BMS and run in brass bushes in the axle boxes. The doors are hinged using 2mm threaded rod
For a total outlay of about a tenner, I'm pretty happy with it but there's certainly room for improvement.