My 21' had a thin panel across the space where it mounted. I had to get a support board for backside of panel. Drill thru the panel, and catch the board with small bolts/nuts. Then mount the swivel using the board opposite as the supporting frame.
After that.. i just removed the entire panel and mounted the swivel on the side of the tv area. Now, i can pass the tv thru the opening for bedrm viewing. Plus better circulation between the two rooms.