My friend Terry built 6 or 7 of something like those for our Boy Scout Troop and Venture Crew. Some minor differences. His has insert-able rectangular stock legs, and both the front and back hinge open, with a divider in the center. This gives you a nice spot to store your propane stove as well as other larger chuck accessories in the back, plus extra prep work area. I'll see if I can snap some pictures of his design soon. Its really nice, all tig welded aluminum. Still quite a chunk to try and handle alone. Best done by two people. The legs store underneath when in transit mode.
I got cha. Yes, I didn't see that most of it was plywood. Ours have fixed tops and both sides come all the way down. It also gives an advantage because the shelves are only half as deep (which means its easier to get to stuff at the back). Plus, then you can put stuff on top as well; usually condiments, paper towels and such end up on top, when its deployed. Let me see if I can scrounge up some pictures. I don't think they are going camping for a while, so the stuff probably won't get pulled out of the trailer soon.
I'm currently thinking up plans for a chuck box, and I love this design - mine will probably be a little less high, as it has to fit under the bed in the camper, but otherwise very much inspired by this one.
Anyway, I was just curious what that drain cap on the side is meant for?