This is a model of a 40' flatcar. The trucks/couplers I suggest for this model are Micro-Trains #954 (Bettendorf Trucks).
I print my models on a filament (FDM) printer. That's what they're designed to be printed on.
For weight and strength the model should be printed at 100% infill. Print the model flat-side down and no supports will be needed.
