I can gather more photos of how the box is attached but in
this google album there are some that show it. I did not use the s280 kit. I had difficulty finding one and did not like that it would have meant the use of chains, rather the cable, as well the chains would have run across the side rather than across the front and back corners. The front cables are mounted to M20 eye bolts that are through mounted on the bed, and the rear corners are anchored with another through bolt that passes through one of the fence stake corners. The cables are mounted to the box at load points that states '14,400 lbs. tensile load per corner in any direction' that information can be
found here. addition to the cables it's bolted down using the dolly wheel mounting points that are on the box with grade 8 hardware. The cables are 3/8" 7x19 Galvanized Aircraft Cables, rated breaking strength of 14,400lbs, the same is true for the turnbuckles that are used to tension it onto the bed.