Figured I'd upload some progress shots as well to illustrate how the joints went together. The wood came as two separate boards whose grain happened to match up rather nicely, so I ran both of them down the joiner to get a nice straight edge, and then through the planer to get them close to the thickness I wanted. After gluing them together and letting them sit a few days I came back, planed them down to the final thickness, and cut the large (about 7'x12"x1 1/8") board down to the individual lengths of the three pieces.

In picture 1 I've laid out all the cuts I needed to make (carefully marked on each board which material I was getting rid of), and have cut out and started clearing the material out of the slots on the left.

By picture 2 I've completed cutting the joints and have carefully cleared out of the gaps with a chisel. Thankfully I left enough material that I can fin tune the fit everywhere. By this point it looks like the side (which is on the table) is just starting to go into the top (which I have clamped to the side of the table.)

In picture 3 I've done most of the fitting, and I can squeeze the side diagonally down to within about half an inch of going all the way. One side is going slightly further than the other, but that's actually just fine and will not effect the final fit.

Because every little distance I squeeze the joint together makes it a ton hard to pull apart because of the extra surface area sqeezing together, I do some final fitting, put some glue in the joint, and toss some burly clamps on it! I had double and triple checked everything so I was (almost entirely) confident that it would go together. Picture 4 shows the result of this. in order to make the pieces slot together diagonally my brother and I were tightening clamps going horizontally and vertically at the same time. Thankfully the result looks pretty good! To make sure the joints would be flush with the sides when finished, I cut them all to be about 1/8" long, and they all ended up being proud of the sides by about that much.

The final picture shows the end result after all the finish work. The ends of the joints were all cut flush, everything sanded down, 6 coats of finish put on with some light wet sanding up to 600 grit, and finally a coat of wax put on with slightly more than an hour before the bench needed to be at the show for set-up!