Highly recommend the Ram OEM "5th Wheel/Gooseneck Towing Prep Group" option for the Ram 3500 (and 2500). An absolute bargain for $400 when you consider the much higher cost to put the same thing in aftermarket. Not to mention your bed will be flat and smooth when the hitch is not in use vs. a universal rail mount which permanently obstructs the bottom of the bed about an inch.
The 5th Wheel/Gooseneck Towing Prep Group supports a 5th wheel hitch, gooseneck ball, and provides an in-bed 7-pin connector (in addition to the 7-pin on the bumper). Most 5th wheel hitch manufacturers make hitches that are plug and play with the Ram OEM 5th Wheel/Gooseneck Towing Prep Group.
Or, you can purchase a Ram or Reese 5th wheel rail adapter (aka "picture frame adapter") that will adapt a 5th wheel hitch with a universal rail mount to the 5th Wheel/Gooseneck Towing Prep Group. The Ram/Reese 5th wheel rail adapter runs $350-$500.
