Seems like I've been down this road before haha. A service tech ended up taking the whole thing off of the side of our coach when our outside TV needed replacing. He cut the caulking and took the whole metal cabinet off of the outside wall. In the end, had I known what he was up to, I would have just removed some access panels from under the dinette area and tried to access it that way, from the inside.
5 years later our outside TV is a little loose with it's mounting and I have been planning on taking a closer look at how it's mounted from the inside.
Good luck with your project, keep up posted on what you find.