Take a look at the Andersen Ultimate Fifth Wheel hitch. It's the best of both worlds.
Rather than putting the gooseneck adapter on the trailer's pinbox where it acts like a cheater pipe on a wrench, the Andersen hitch mounts to your existing gooseneck hitch in the box. You attach a small adapter to the kingpin on the trailer. Now you have the flexibility of a gooseneck without putting excessive stress on the trailer's frame.
I know, I know... There are some people out there who use gooseneck adapters on their fifth wheels and claim that they have "no problems." They also haven't encountered that "Murphy" situation, such as the trailer sunk in the mud where it would be subjected to a hard pull.
Here's what happens when you put a cheater pipe on a wrench and submit it to a hard pull:
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