Scott-
If it is a single wall roof, you might be able to mount it by using some exopy or JB weld to adhere some nuts to the roof. I am sure that a tack weld would burn the white paint on the other side of the roof, but hey who sees the roof anyways?
Another option to mount the monitor might be to fabricate a bracket using the existing screw holes for the visors, and rearview mirror/light assembly, and the over head lights assembly aand make your own double wall.
(I am assuming you are puting it up in the location of the rearview mirror location.) Just some ideas which I am sure you have thought of.
I am looking into a visor option to put on my list of mods, but am not sure if I want to block the view a head. My other option I have been playing with is in the stock radio location, either double din or a single din flip up. But hey its down the road a ways.
Well let us know what you come up with... I am sure interested in this one!
Wil