My Itasca is pre-wired for a TV in the bedroom. My opposing wall is the shower also. I pulled the panel off the wall, where the connections are located and they put wood backing plates in the wall, where the mount should be installed.
Your MH most likely has something similar. You can feel around for signs of backing plates, or try to remove whatever is covering the area where your TV should be mounted, for a better idea of where the mount should go.
I just took a pic of mine, but I'm having issues loading it. You get the idea anyway.
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2014 Itasca Spirit 31K Class C
2016 Mazda CX5 on Acme tow dolly- 4 trips ~ 5,800 mi
Now 2017 RWD F150 with a drive shaft disconnect