I was thinking of boxing / reinforcing my CrewMax frame and adding a tray to fit a camper for a 6.5 ft bed, kinda like this one. Not anymore!! I think I read they even did some work to stiffen the frame as well.
In that video you can see that he was heading into the setting sun, and probably driving way to fast considering that he was blind. He hit something hard enough to bash in the skid and radiator as well as kink the rear of the frame. The kink is right at the forward bed mount where the frame starts bending down, which is also at the very front of the flatbed. This location is on the weak and flexy open C part of the frame (everything aft of the forward leaf mount).
I didn't see any evidence that the frame was reinforced. He shows the truck with the bed off here:
and in the next post a few days later the Norweld tray is on. Welding on the frame would require removing everything... and on the shortbed Crewmax you'd need to remove the cab as well if you were boxing all of the open-C part. Major job.
The Norweld tray is very stiff torsionally, while the part of the frame that it is mounted to is designed to flex. This increases stress quite a bit at the transition, which is at the forward bed mount on this rig, which is not a strong location. In fact I've heard that truck frames are designed to collapse at that point to reduce deceleration in rear-end collisions.