You can fit the original tail light panels to the replacement fibreglass guards and sit into position. Slowly close the front doors and mark where the rrear of the front door panel touches the ute guard. You will need to allow a 6mm to 10mm gap between the rear of the door and the new panel. Normally we would match the gap off the frint of the door to the front guard.
The rear panel is screwed into position the same as the original. Reuse the speed clips and screws.
End fill in panels are also supplied to fill in the gap between the B pillar and the glass guard. This is normally sickaflexed into position once the guards are fitted for the last time.