I built this Knight hauler into what resembles the Coronado 122 day cab and added a 26ft flatbed with headache rack. The truck frame rails were stretched and extensions added behind wheels, and a dot bumper installed.
The flatbed is aluminum with wood decking , it is built sturdy with plywood sandwiched between sheet aluminum. The bed is held on by the u-bolt you see in the picture, clamps around bed frame rails and truck frame rails.
I may make some of the beds to sell, they can be made to different lengths, this one is 23.2″ long.