Are you attempting to mount on an outside wall, or on the back side of the entertainment center facing the living room?
If you are wanting to mount on an outside wall, just get the wall thickness at the main entry door. If you are looking to mount on the back side of existing entertainment center, but have a television facing the bed, then... as suggested above, add an extra thickness of lumber for better support. If you are screwing from the bedroom side into the existing entertainment center, even if you went completely through, the other end of the screw would be hidden by the existing television in the living room.
2017 crossroads volante 310bh: