It kind of depends on your trailer wiring. Everyone seems to be different. On my latest trailer I need to disconnect the coax in the bedroom and reconnect it to a different port when I use cable. (took 6 months to figure that out) Really a dumb system. The trailer before that was equally complex. What I did was to run coax from the source (campground outlet) in my door and connect it to the TV. Once that works, gradually work it back to the outside of your trailer. My current trailer does not have the usual A/B box, my previous trailer did.
