I can't weld, but can run a rivet gun and assorted other tools. I could see building this box, using diamond plate, some "L" angle aluminum and piano hinges, soffit vents, etc.
I've bought diamond plate from these people: Metal Supermarket
, cheapest price in Portland (any size/quantity) and are only about 20 blocks for my house (at most). They have a number of stores, check to see if one is in your area. I like buying from them, because they'll do all the straight cuts I need.
Course, by time you get done, it might be just as cheap to go to a Parts & Auto store and buy one