Here is a detail of how B&O Gondolas on excursion trains worked:
Brother, Sis and wee-gazer. I don't remember how the steel floor-plate was attached but I remember being intrigued with how it moved when the train went through a curve. It's a bit hard to see but there are railings attached to the floor plate and then chains strung from those railings to the railings in place of the removable car-end.
