Try a Winegard Sensar Pro.. Works even better
And upgrade the Omni (or optionally upgrade it for best results) to a Winegard Sensar 4
Put the Sensar 4 up there, run coax to an A/B switch and then you can switch between them.. The Sensar Pro supplies 12 volt to the mast-head (inside the antenna) amplifier, ONly switch the switch when Sensar pro is set to Cable (OFF)
Part of your problem may be low-cost cable in the RV, Most manufacturers use lowest bidder which is always high-loss RG-59 Replacement with low-loss RG_6 will often improve performance. Epically if it's a long run.