The not always a joke about Omni Directional Antennas is "They work equally bad in all directions"
For RV use I would recommend scrap the omni on the roof and put in a Winegard Sensar IV with the optional Sensar Pro Wall plate... This is one you crank up and point.
or you can get any number of fairly good pole mounted... Put 'em up 20 or 30 feet on top of a flag pole and again a directional antenna is your best choice.. that flag pole can be a touch costly though
But a high gain antenna at height can't be beat.
