In addition to the Sensar Pro shown above there are two other things (or 3) I would check, Some of this is from experience.
The Wingman add on for the Batwing turns it into the BEST TV antenna marketed for RVs bar none. About 30-40 dollars and you can install it yourself, a pair of pliers is optional as the only tool needed.
THe Sensar Pro (ALready described by others)
The coax Roof to antenna. #1 problem on "old" RV's is this coax,. it is exposed to sun and weather and it goes bad... NOTE: there is a connector either at the roof. or in the roof.
From Experience.... that connector.'
Blown fuses.
FInally a comment.
THe batwing is directional (Basic batwing is a figure 8 pattern) Fairly narrow beam.. IF you are "Surrounded by TV stations" Rabbit ears (Omni-directional, means they receive from any angle) work better.
There are additional possible issues like bad wires and switrches but in independent lab tests the Batwing beat all competition .