If you want to simplify things a bit, you can build or buy whatever kind of field box you want, and then use a folding luggage carrier (the kind that looks like a dolly) to haul around your box. This way works well, is cheap, and doesn't take up a lot of extra space. You can pick up a luggage carrier for around 10 to 15 dollars at department stores.

Just another idea.

-bsc