The R2 frame consists of 32 pieces; all but one of those pieces are made of wood. The $150 frame (prices vary) gives R2 stability and strength, and it provides a surface on which to glue the aluminum skin. It's relatively lightweight - maybe 10 pounds.
Each piece has been carefully sized to match the original R2 unit. To connect the pieces I used Elmer's Wood Glue and screws. The pieces had to be clamped together while the glue dried overnight. I didn't dare attempt to move the frame until the glue was completely set.
As you can see in the photo, the frame is sturdy but it allows for a door and other openings for lights and accessories. The next phase will be painting the frame.