Can anyone advise if there is any wiring,piping etc in the side walls of the bay storage areas?
They are very solid "feeling" so I suspect not because of the central cable tray running through the coach.
On the passenger side 2nd bay from the front is a cable outlet and power outlet on the front wall.
I am mounting a MORYDE tv mount on the rear wall of the same compartment to install a 43" Sony TV and want to relocate the power to the back wall and run ethernet cable for hdmi over cat6.
I don't know for sure the answer to your question about wiring, but I would guess that there are not any wires buried inside the bay walls. In our coach, all the electric wiring in the bays is out in the open on the surface of the ceiling or the walls.
When you install your TV mount you should try to bolt it to one of the metal frame members in the bay wall. Would make it much stronger. I cut a hole in a bay wall to get acess to the area behind my water heater. I posted some photos of the cutout in the wall that show the construction. Link below.
My post also contains a link to a simple little magnetic stud finder that is very handy for finding the metal structure in the bay walls. Photo below shows another version you can find at most hardware stores.
Behind the Water Heater Access Port (https://www.foreforums.com/index.php?topic=37421)