Standard non 5th wheel Heartland Trailers wired for TV will have a Cable connector with weather cap on the outer wall of the trailer and a CATV connector with red on/off button with red led inside the trailer where a TV would go. There is a factory coax run between the outdoor connector and the inside outlet. The inside outlet has red button that powers the roof top TV antenna and disconnects the wire going to the CATV connector, with the red LED indicating this. With red LED off the connector is tied to the outside CATV jack. If you don't have any CATV connector on the outside of your trailer, than you will have some DIY effort to do.
The 5th wheels are more complicated with multiple TV outlets and I don't discuss here since you asked about the MPG.
When on CATV you will have to go into the TV menu and put into CATV mode and when on OTA antenna you have to go into the TV menu and put into OTA mode and newer TVs you have to scan in the channels when you switch back and forth.
Regards,