I can't answer many of the questions, but have owned a 1988 5th wheel, 1996 camper, and 2008 camper. I think the newest does have more wood. I don't know if the fiberglass thickness is any different, the new one isn't all that thick and they are chopper gun layup so you really can't go too thin either. The 1988 and as I remember the 1996 ones had XPS foam while the 2008 has EPS foam ("bead board"). The XPS could be used sort of as a structural core, while the EPS really can't. I doubt the fiberglass can support the shell without reinforcement. On the newer ones they seem to be relying on wood stiffeners glued to the shell, and the interior panelling making of the second skin of the sandwich.