I know little about your particular RV, but your problem probably lies in a failure to turn off the signal amplifier. Their is a very small switch located next to the coax connection. The light is green if the amplifier is on and red if it is off. It should be off if you are using cable. It is only to be turned on when the antenna on the roof is being used.
Jim in Memphis
Wife of 48 years is Brenda
2019 F450 6.7 Powerstroke
2017 Mobile Suites 40RSSA
2015 26TBUD Salem Forest River (For Alaska Trip)
2001 Road king w/matching Harley sidecar