There is a couple different choices
1. The adapter that many dont like but you will see farmers using them on the fifth wheels for YEARS and never have a problem. The fact that the etrailer rep will still recomend them says something. They are the cheapest way to get to a gooseneck ball in your truck.
https://www.etrailer.com/Gooseneck-a...l/CAB-C5G.html
2. Andersen ultimate hitch. Leaves your fifth wheel hitch in place and simply puts a adapter on the end of your fifth wheel pin box and a raised gooseball in your truck. Super light and easy to use. Been running one myself for years with zero issues.
https://andersenhitches.com/Catalog/...onnection.aspx
3.A total pinbox replacement with a Goosebox type setup. There is a couple different choices for these. A Gen-Y and reese goosebox. The best riding choice of the 3 and the most expensive. But still far cheaper the the boat anchor traditional hitches.
https://www.etrailer.com/Fifth-Wheel...5-GH-8045.html
https://www.etrailer.com/Fifth-Wheel...e/RP94720.html
Also dont put a lot of stock into the frame warranty stuff. First that warranty is limited as it is and if you didnt buy the camper new chances are there is no warranty on the frame.
Next the reason behind it is more more about money and shafting people then it is about products hurting their frames. LCI is the exclusive provider of the reese goosebox. So to increase sales of the goosebox they made all other hitches warranty voiding. It also gives them an out to shaft over people who might have a frame warranty claim. Because even if you did run an adapter and hurt the frame there is no way they could ever prove the adapter did the damage if you removed it before taking it in. But you can bet they have not paid many warranties by using the "looks like the used an adapter BS". Even if it wasnt used.
I love my Andersen but my next truck will have a flush mount gooseball and I will buy a gen-y or goosebox just for the cushioned ride they offer over the andersen ultimate.