I need a physical, letter-sized inbox that:
* Stacks two high
* Is completely open on the edge, no lip
* Faces "sideways" (e.g. the long edge is the open edge)
* Is as enclosed as possible on the side so papers can't fall out
* Is as heavy as possible, because my cat likes to push it off the desk. Plastic, mesh, lightweight metal are totally out.
It's the last one that's hard to find these days. Anyone have a set they like that they could recommend?