Perhaps the 3M “Command Cord Bundler”? Easy to stick on when you get where you’re going and it will easily support your cord and take the weight off the port. Easily-removable and the ‘stick’um’ tabs are cheap. Won’t leave a mark on your camper. (Only works on smooth surfaces.) Might even hang on at highway speeds if in a sheltered spot? I’ve got the same setup as you (i.e., Zamp and port) but hadn’t considered the issue. Perhaps I should!