In our previous Trail Runner TR22RK, the backer plates were marked by stickers over them.
However, the bedroom sticker was off by over a foot . . . so I had a couple of unwanted holes in the wall.
If you press on the wall in that area you should be able to find out exactly where the backer plate is.
That is how I found them in our new Prowler.
Will be getting a larger TV for this spot sometime soon!