Take the tailgate off.
You will want to extend the ball behind the camper. It allows you to turn sharper, go thru "dips" better, and it's easier to hitch and un-hitch.
For a short extension like an 18" then most any extension rated for the weight will work. If you need something long like 24" or more I would use the TorkLift Super Hitch and Super Truss.
When I towed my 4,500 pound boat behind my truck camper I started with a Curt 48" extension in the factory 2.5" receiver. It worked. When I changed to a dually truck with only a 2" receiver I decided to upgrade to the Super Hitch rather than just change to a 2.5" receiver. The Super Hitch is a much stronger device with much less play. It also has a larger tongue weight rating and a larger tow rating. Not that you need them but it's nice to know you have the extra capacity.
No matter what you do, you will be over the GVWR of this truck. If you can stay under tire and axle ratings you will be fine. You will likely need air bags, HD shocks, maybe a rear sway bar, etc.