Bob,
I don't think you'll have any luck trying to pull the cable through as they probably have it going through cable clamps or have the wire bundles tie-wrapped along the way. I'd try 2 things first; run a cable outside the coach to the tie-in point above the passenger seat and see if that improves the signal quality. If so, I'd then replace the connectors on the ends of the existing cable as most poor connections occur there. If it doesn't improve the quality, then check the cables/components from there to the TV. If still bad, you're probably looking at figuring out how to run a new cable.
Steve