I'm not expert but there isnt a hell of a lot to those walls in a motorcoach.... outside fiberglass, fairly thin metal struts, insulation, inner thin "sheetrock" wall and that is about it. I dont think that they would have that massive TV mount bracket installed into the solid wood of the fireplace on a "B" if they could have simply installed it t o the wall of the coach. I'd give that a lot of thought.
You might be able to reposition the holes in the fireplace top to accommodate your new TV and install a bracket that lets you pull out the TV and tilt it left or right. There have been quite a few owners that have made that mod and they have added that tilt / swivel bracket to the already installed bracket.
Gary and Dee, Zowie and Bowie (traveling cat sibs)
2019 Cornerstone 45B, X15-605hp, Imperial, Spartan K3,
2013 Honda CR-V toad, Demco Excali-Bar II,
Demco Baseplate, Demco Toad Light system, 73 de W5FI