Hi Lewis, We have the same problem with our wagons when loading and unloading. It isn't a solution but maybe it is something you could try. I developed a safe system of work in conjunction with the drivers, which they signed and agreed to. Basically when the trailer is empty, the curtains must be closed and the straps must be tied. When loading or unloading, the drivers must tie the straps to the trailer itself. I am not too in touch with trailer types but the straps we have attach to the trailer even when it is empty and there is no load. The straps still move about a little but nowhere near as much if they were loose. Our drivers will take a strap at a time during the loading/unloading process and secure the load, a pallet space at a time. I am not sure whether that is a similar setup to what you have, but maybe you can take some assistance from this.