I have posted this here before, but I see you are a new member so here it is again.
When I was first looking at getting a fifth wheel I asked my local mom and pop camper dealer about using a goose neck extension since I already had a goose neck ball and his exact words were "Don't do it to a camper you want to keep." He went on to explain the build differences between a goose neck trailer and an rv frame. This was 15 or 16 years ago, and I took it to heart and will never use one.
The fact that I had been a truck driver for 17 years also made me appreciate hooking up to a fifth wheel plate as opposed to a ball mount.