If you look at the profiles for the elevator, rudder, horizontal, and vertical stabs, you'll see a 1/16" gap between the upper and lower sticks. It looks like there is a top and bottom frame. The only way I can see this structure being stable is with the 1/16" sheeting or plywood between the top and bottom.

Alternatively, there might be 1/16" stringers running fore and aft, but without cross bracing, it would be pretty flimsy.

Brad