Hi, McMan!
Try KZ Customer Service @ 1-866-472-5460. If Cust. Serv. does not know the answer, ask them to contact Design Engineering on your behalf for "what's behind the wall".
Perhaps, you might find the desired location of the mount, drilling a small hole to determine thickness of base material. Plan to use toggle-bolts (expanding bolt assembly), with small fender washers under the outer bolt/screw heads, as needed.
Hope some of this helps.
John