Hi Steve
I use the Anycubic M3 Max. The cars are about 14inches long and need to go in slanted. They are comparable to D&RGW 6500 series flats.
I use brass profiles to strengthen the car. I glue the profiles into the slits and then glue a brassplate on top. This will carry about 6lbs without any deformation.
For smaller parts I have a Anycubic Photon Mono 2. There I print the detail parts.
The great thing is that all the details are already printed on the sides of the car like stake pockets, etc. The brake cylinder and rigging, for example, is one part with all the details.
Best, Christian