On our 2018 Road Warrior the exterior wall is aluminum frame, the inside wall is wood. We had to have a sidewall crack repaired, and when they fixed it, the frame was aluminum. Once when we had to move in a campground, we forgot to double check that the bathroom door was closed before we put in the bedroom slide. The slide pushed the wall and knocked it out of place. When I repaired it, the interior supports were 2x3 studs.