Clever idea to use the cardboard boxes reinforced with wire. If the inner ones break down too fast, get more boxes and put them on the outside, tied together with twine. The very best boxes for this might be those from furniture and appliance stores. Larger boxes have fewer seams and gaps. The big ones are also ideal for killing the grass and weeds when starting a lasagna bed. I like the old sink idea: very sturdy and it comes with it's own drain.
