This is perhaps the most innovative model I've yet built. It features a specially designed 3-D printed locomotive frame. The frame was designed with .001" tolerance to allow the NWSL Stanton drives to be supported well, have clearance and for the model to sit at its correct, prototypical height above the rails.
In the photo below, the center black chunk of plastic is the speaker baffle. Lead weights cover the 3-D printed plastic frame, the Sountraxx Tsunami TSU-1000 sound decoder providing control for the stanton drives and the sound system. (iPhone photo, forgive the grainyness)