Here a good link on the subject.
https://www.etrailer.com/question-21804.html
I think I will get the Fastway Universal Trailer Coupler Lock for 1-7/8", 2" and 2-5/16" Couplers DT25013 for my pop up camper.
I was thinking about using a cable threaded through the wheel slots and trailer frame with padlock. Does any one know if bolt cutters will cut a cable? For that matter a hack saw or cut off wheel will go through most any thing. The cable is probably not such a good idea.
bt