Yes Momo on GL and other GL users have a variety of cereal and other food boxes as hay racks. Just NEVER use boxes that are refridgerated or frozen as they have wax and chemicles on them so they don't melt from the moisture. I'm assuming since these boxes cannot be recycled that they probably would not be healthy to let the piggies munch on???
Very cute I was thinking about doing this today as well. I find if you cut a small slit in the box you can take a black metal paper binder (the 1 inch or 3/4 inch not sure) sized clips REALLY help keep boxes and stuff on the grids better...