I am currently rebuilding a 90 Coachman Catalina. And mine is all aluminum frame with foam filler with wood laminate on both sides.
The only other place I see wood is around the windows and on edges mainly just for screw strips
As you can see on the front, foam and aluminum frame, on the side the wood was in the corners, everywhere else you see wood on this was once foam, the aim was to beef it up. Hope this helps