Due to FCC regulations, the broadcast signal for local channels may not be available in all locations. Your local channels are delivered via a spot beam satellite that targets areas immediately around a city where you live, like a spotlight. If you leave the spot beam area, your local channels will no longer be available.
Example: If your primary receiver is in Tampa, FL, and you are in an RV in Seattle, WA, the RV receiver won't get local channels, because the satellite transmits signal only to the area around Tampa, FL. As soon as you drive your RV inside the Tampa, FL, spot beam area, you will be able receive the Tampa locals again.