When we were up in South Dakota with our old 2013 Heartland Trail Runner, I finally got frustrated with the flickering picture we were getting (and our dealer couldn't seem to figure out after a couple of tries at it), so I borrowed a ladder from the campground (thanks Big Pine's in Custer) and pulled the coax up out of the roof to find that the coax connector just below the roof was bad.
A trip in town (Custer, SD) to Shopko (love that store) where I bought a coax crimper tool and a supply of connectors and fixed the problem once and for all.
Our previous Trail Runner at Big Pine's in Custer, SD:
We had a lot of issues with the coax run in our new Prowler as well, and after our new dealership's service department showed that they don't quite have TV and cable coax wiring skills, I also had to go in while out on the road camping and fix it once and for all by myself.
My own opinion is this (and maybe someone here knows otherwise) . . .
I think that the coax is probably run while the frame is upside down in the factory before walls and a lot of other stuff is installed, and it looks to me like the coax is wired up backwards from the wiring diagram since the frame is upside down.
At least this makes sense as so far, as both brand new RV's that we've purchased had the coax wired up backwards.
And it started right at the outside wall where the cable-in connection was hooked up to the output at the very first spitter in the run . . . and not the input of that splitter.
And splitters are one way . . . in other words, the signal can only pass through to the output from the input of the splitter.
Also, check the built-in stereo to see if the radio antenna is connected to the coax splitter.
If it is, try unhooking the radio antenna from the splitter as that was causing our living room TV cable signal to short out and also was affecting the TV signal from the roof antenna in our Prowler as well.
I now have a boat antenna (provided by our dealership) hooked up inside the entertainment center for the radio, which is great for FM . . . but doesn't pick up any AM stations.
Still trying to work that one out . . .