gulfstreams have plenty of metal framing in the roof, though even more would not have hurt. The rear wall is likely mostly wood like any other model, not sure whats going on there. They had ladders, so presumably some support structure was embedded, cant say for sure since its been a while since I saw the back walls undone. There is a set of videos of the deconstruction of an 86 conquest by a forum member on youtube that should provide definitive answers.