The two boxes are taped together and the flaps folded over to make a platform for the third box to go on top. It is a smaller box with a hole cut out of the bottom to attach it to the structure.
Here is a picture of the finished apparatus. Mind you, it is not fully duct taped, nor has it been tested by my expert R&D crew back in the USA. It will be on the testing block come Fall when classes start up again.
P. S. I would have loved to get out the hotel in Edinburgh to see the sites, but on the way in I popped a tire on a sharp curb. I was not going to go driving around the city after that. Building in the hotel room was good therapy for me.
P.P.S. If you want to see how someone is using the ideas in this blog in a really unique way, check out Juliet Robertson's latest post at Creative Star Learning called: The "Sensori" Water Station. I am blow away by her ideas. They are much better than the piddly little box structure in this post.