Started off with a 2x12x96,
cut it to 64.5” leaving the line, do NOT split/take the line, still works, loosely.
cut corners @ 45° , 2.5” from each corner to form the diagonal line to cut, so it sits down against the bed of the truck:
Two adjacent corners, on long side (one-way), or
All four corners (doesn’t matter which side is down).
I may go back and rough it up, repaint/plasti-dip it.