Well the boxes, according to my informant, are not stacked áccording to regs'. The bottom layer is mounted on two concrete sleeper like thingys each placed on the grassy ground of the park (which has seen about 3 years rain in the last 3 months... - remember those world wide videos of The Toowoomba Inland Tsunami? - that's the park it went thru mate!), and then two of those are placed on top of the first box, and the second one placed on top of that. Not as stable as 'designed', I think....

:-)