newer truck for 5er

I used this on a previous truck. Be sure you get the correct shank...round, square, etc.
Prices listed on Curt's website are MSRP. I bought mine for much less at Amazon.
https://www.curtmfg.com/Category/57/Gooseneck%20Adapters

Depending on the brand/type goose neck, you can get an adapter with rails, to fasten into the GN hole. Then just set your hitch on it. Look at E-trailer for options.

Jerry

If you're talking about a gooseneck adapter that bolts on the trailer's pin box and sits on a gooseneck ball in the bed, DON'T DO IT! Fifth wheel frames are not made to take the torsional stresses that the "lever" of a gooseneck adapter creates. If you're talking about one of the several hitches (B&W Companion, Andersen Ultimate, PullRite UltraLite, etc.) that mount to the truck bed using the gooseneck ball but are not true gooseneck hitches, they are all excellent choices.

You don't mention what year and model your fifth wheel is... just be aware of cab clearance issues pulling certain fifth wheels with a short bed truck without a sliding hitch.

Rob