I believe that the sidewalls are there to protect pedestrians, cyclists and small cars from getting run over by the rear wheels. That's why they are flexible. You see these often on European trucks.
?? Which part are you talking about?
I'm talking about the main side walls of the trailer, above the wheels and such. The part that has "wagoners trucking...." and logo bit printed on it. They likely roll it up to safely remove the cars inside....
Time is the best teacher. Unfortunately it kills all its students.