Contact the manufacturer with the serial number and other id information. They can probably give you a good ides of what is in that wall. Who is the manufacturer, and where are they located. I have doen this with two cifferent manufacturers, and they have been very helpful. One even had a blueprint that the coach was built from. Of course, there are those days that something didn't fit just right, so they just made do. Worst case you might have to go into the back of the wall and add supports. We don't have inside steps, but the grab rails by the outside door are essential for us.
Noel and Betty Johnson (and Harry)2005 GulfStream Ultra Supreme, 1 Old grouch, 1 wonderful wife, and two silly poodles.