If I were regularly using a goose neck hitch in my ranch operations, and needed to occasionally haul a fifth wheel trailer, my preferred choice would be the B&W Companion, even though that means hauling the fifth wheel hitch in and out of the truck bed.
But most of the folks I know around here simply put a goose neck adapter on their fifth wheel trailer. Ratings range up to 20,000 pounds (which is really heavy heavy for a RV fiver) and quality varies. Convert-a-Ball might be the best, but relatively expensive. Nobody I know who has done this has broken their fifth wheel frame, but they've all had Carriage trailers, and Carriage is probably above the norm on fifth wheel frame quality.