[MrForbes]

Also remember that you want it to weigh LESS than 400 lbs, with the robot (and whatever other stuff) inside. You can use slightly thinner plywood, 3/8" is the minimum I would use. And you can possibly use 2x2" pieces of lumber instead of 2x4s, but they would more likely to split.

If you study the picture I posted above, you'll see that it is designed to be built as several subassemblies (and can be disassembled into those subassemblies easily). The sides each have four 2x4s screwed to them, the top and bottom have two 2x4s on them, and the rear and (removed) front panel are just plywood. There is a lip along the bottom where the plywood extends past the rest of the crate, so that the front panel can rest on it to make it easier to hold while screwing it into place. The bottom has additional 2x4s to support the frame of the robot, the wheels sit in the recesses between the 2x4s so that they are not touching the crate...that way, they won't be damaged by rough handling or rough roads.

I think you might also need some 3" long screws to attach the sides to the bottom, and for other miscellaneous uses.