Place lug nuts on the tray like so. 

Using M8x25 bolts with a spring a flat washer, fasten you guard to the tray.

Move the guard in to position, making sure it is not touching the cab and is centred with the tyre. 

Once your guard is in position, fasten all bolts. 

Double check that your guard is located evenly along the length of the tray.

 Repeat these steps with the guard on the other side.