I had one flat car load of forklifts that kept shifting with the curves and ultimately became unbalanced toppling the car. So, I super glued them into place. Recently a purchased an older K-Line circus car with circus vans on it. They seem to have a slight propensity for motion. I am thinking about making them "permanent freight" as well.
Any of you glue your loads to the flat cars? Properly done it is invisible.