Here is a box in operation (Rapide Nord L. S. Models coaches and steam boiler van Hornby-Jouef). There are foam shims to prevent the cars from moving along and rubbing against the dividers.
Warning: these shims must not bear on the couplings!
Warning (bis): some fragile details can be broken when storing a vehicle (I had the problem with the shutter handles of an OCEM wagon). In this case, it is better to leave a plastic film wrapping the model. Same for models too low to be grasped easily, like flat wagons.