RV cable systems can be a nighmare, particularly if modified by a previous owner.
Question . Have you tried to get park cable in from the , hook up: usually in the power cord bay to the TVs ?
The reason I ask is , many RVs have a cable /antenna booster switch , in the system and that switch will not pass any kind of sat. signal. Park cable , will go through.
The switch, has a cable hook up on the front, 12v lighter type socket, a small "on" button and an LED indicator light. The on , is to power up the booser in the antenna.
If you have this switch and want to feed sat. signal through you have to by-pass it.