I had a broken front pinbox support beam on the previous trailer. It was also after being towed due to my truck breaking down. The tow truck installed a GN adapter and took off with my 5th wheel. He used his Jake Brakes instead of his regular brakes to slow the truck down and I could see my pin box moving and told him to use the brakes instead but he never did.
I was lucky to make it home from Florida, but after I noticed the pin box no longer level on the hitch, I took the front cap off and did the repairs. After calculating the strenth of all the beams, the very front beam that holds all the load was at 100% load with no margine of safety left. Its true that these are made for least amount of weight while fexing within the allowed limits. Mine flexes and I do watch it very closely. No way would I put a GN on my pin box. Maybe with a shorter extension might work out but after my experience I will stick with the designed system, like the real truckers use solid 5th wheel attachment that do not move while towing.
The 5th wheel pins on a camper are attached to a beam across 8 ft and they flex. The GN trailers have an A style Frame that does not flex and solidly build to allow a longer reach down to the GN Ball with heavy gussets that holds the heavy walled pipe.
Everytime I see a GN setup on a 5th wheel, I get a scary feeling for the owner driving on the highways with a dangerous. unapproved setup, that like mine , can fail and cause extensive damage.
I am not the only one that broke the pin box frame, I hear of those failing all the time, specialy if the TV is oversize for the camper, that has been happening here many times driving on north hyways that have been exposed to freezing weather in the winter.