Not many 5th wheel trailer mfg recommend a GN adapter. I think some of the heavier built trailers are designed for using a GN adapter and even have it as a option. Your brand trailer mfg can best answer that question.
You can add something the Reese goose box system.
Or do like many who pull GN trailer is go with a different style hitch like the
clicky link PullRite.
or the same style
clicky link Andersen.
I have a Reese above bed floor GN style hitch, similar to the Curt, I use for my GN trailers. That way I can use it in the wifes 1500 chevy or my other trucks.