teacher art and design project joining large cardboard boxes?

I am a teacher and my students and I are planning on making a large(child life size) model of a robot out of several boxes and then covering them in foil. However has anyone got some good suggestions on how we could join the boxes for maximum effect. The 'robots' would have to be free standing.
I was thinking of using split pins/paper fasteners in each corner of the boxes we join but i can only find them of size 200mm-anyone know of any bigger ones or something i could use instead.
Thanks

cut strips of cardboard 2 inches wide and 6 inches long. poke a hole thru the box and the strips with a Bic Pen and simply use 1 inch long screws with washers and nuts. Your robots will never fall apart.

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