The cable from outside and the cable from the roof top antenna converge in the back of the coax connection inside. There is an electronic splitter/ amplifier combo on the back side of the face plate. This device will not allow satellite signal to pass through. To get around this, remove the box and figure out which cable is coming from the outside connection. Remove the cable from the splitter. Buy one of the plates from the link below or similar, then remove the coax jack from it. Drill a hole in your existing wall plate amp combo and insert the new coax jack. Connect your outside cable to the new jack, re-install the wall plate amp combo. Use the new jack for your dish receiver.
Now, on to other guidance. A joey will not work in your camper. You need a receiver called a Wally. It is stand alone and works with the portable dish's. You can add this to your account, leave it in your camper. You just have to wake it up from the Dish app if it's been awhile since you used it. It works well with the tailgater's and does what you'd expect.
https://www.amazon.com/Mediabridge-W...90659160&psc=1