Recommended Slider Base and Ram Puck System Adapter for a Curt A20 5th Wheel Hitch Head  

I’m not sure I already had a sliding hitch

Jerred H's response is correct. When I switched from a Ford long bed to my '23 Ram short bed I did exactly what you are wanting to do. However, that rig ended up sitting in my basement due to a few disadvantages. First, there is much debate as to whether a slider hitch is even necessary. I have a '22 Keystone Cougar and have found the curved nose cap has enough clearance to eliminate the need for a slider. Pretty much only 5ers with a straight cap are in any real danger of contacting the truck cab. One advantage to using a slider is to be able to move the hitch back prior to hooking up. This allows you to approach at more of an angle without the tailgate impacting the camper than would be otherwise possible. I've stayed in a few campsites where this was a real benefit. There are however, disadvantages: Weight - this rig is very heavy. I had to use an engine hoist to put it in and take it out of the truck. Even separated into two sections it is just too heavy to move easily and it really eats into your cargo carrying capacity. Mechanical linkage - there are lots of moving parts that allow the rig to move around. Every standing start or deceleration results in clanking movement much like a train starting and stopping. It's noisy and inefficient. As I said, it ended up living in a corner of my basement unused. What I did, and should have done from the start, is order a Reese Goose Box from eTrailer. This is a real game changer. I also purchased the B&W Ball and Safety Chain Kit for Ram Underbed Gooseneck Trailer Hitch Part Number: BWGNXA2062. It comes in a plastic case that stores easily in the front of the camper. If you feel you need that extra space between the camper and cab, the Gen-Y Hitch Gooseneck Trailer Hitch for Dodge Ram OEM Puck Systems - 5" Offset - 25,000 lbs Part Number: GY83XR is a great option. It's not as easily stored as the B&W but will give you peace of mind and is much, much lighter than a 5th wheel hitch. Towing - the Goose Box is quiet, so very quiet that I was able to hear the whisper of the safety chains against the spray in bed liner in a turn. I thought something was wrong at first, but it's just that quiet. The connection between truck and camper is immediate and secure. When the truck moves the camper moves at the same time, not seconds later. Hooking up - the socket on the Goose Box is "cone" shaped so you don't have to be any more accurately lined up than you do with a traditional 5er hitch saddle plate. I've tested it up to two inches off center and it slid right in and locked in place. The airbag in the Goose Box is a real benefit as well. I use airbags under my 2500 so already have an air pump handy when I hook up. After hooking up I add air to the Goose Box until a white line is centered in the sight hole. Done and done. Here's a final "hidden" advantage: If, heaven forbid, anything should happen to your truck while on a trip, you would be severely limited in your choices for a rental to get you home. With the Goose Box any truck with a goose neck socket will work for you; vastly increasing your options.