The "old" RPO-Combine, Coach and Observation cars were originally manufactured by Sekisui Kinzoku (aka Kato/Japan). I'm told by Charlie Vlk that the tooling for the newer Con-Cor-made RPO was damaged fairly early on, and as a consequence, very few were made. Although the mid-train dome is technically a "corrugated" car, it was also included as part of this smoothside series. These cars are all based (more or less) on Great Northern prototypes from the late 1940s / early 1950s.
Baggage-RPO Combine (tooled by Kato) -
Baggage-RPO Combine (tooled by Con-Cor) -
Mid-Train Dome -
Micro-Trains also sells the Con-Cor smoothside baggage cars, diners and coaches as part of their Ringling Brothers Circus car set -