Regular tubs do not hold 'craploads' of dirt well. The plastic is so thin that they cage will bow out in all sorts of directions..it is really arkward trying to fit a top on something all bent out of shape. If you are looking for something temporary, Rubbermaid Roughneck tubs are less brittle than most others and I use them for baby housing with about 7" of soil. They have two types...try to get the one with the flattest bottom. Ridges on the bottom can cause cracking once the dirt is put in. Baby housing is all they are good for though and will be useless after the monitor reaches about 8-9 inches.
I have built several different 'plastic tub' cages and have learned from experience what can and can not work. Let me know if you have any questions.
I will try to snap some pictures of my small cages this weekend.