I simplest solution would be to use what I already had lying around.
I made this at Techshop.
Step 1: Cut List for the Wood
Side A: 9"x 11" Quantity = 2
Side B: 5.5" x 10.5" Quantity = 1
Side C: 5.5" x 11" Quantity = 1
Top: 6" x 8.5" Quantity = 1
Bottom: 5.5" x 8" Quantity = 1
I cut a 4' x 11" piece out of my scrap on the table saw, then used a miter saw from there to cut everything down to size.
Using the table saw again, I cut a dado into both "Side A" pieces 1/4" wide, 1/4" deep. 1/4" from the top (along the short side).
I also cut a rabbet into the "Top" piece 1/4" wide and 1/4" deep along both long sides.
This is so I can easily slide the top on and off.
Step 2: Assembly
I first clamped the two "Side A" pieces, the bottom piece, and the "Side B" and "Side C" pieces together, and put a couple brads in to hold it in place. Make sure the "Side A" pieces have the Dado on the top.
Remove the clamps and add more Brads to hold it all together long term. I ended up with 14 brads total, 7 on each of the "Side A" pieces. 3 along the bottom and 2 along each side.
Now you can just slide the top piece right in. If its a bit too snug, you use the dado blade set up or sand paper to remove a bit more material.
Step 3: Sanding
Its not going to look the best it possibly can, but this was scrap wood to start with. I just needed a quick way to crank out these boxes so I can spend more time on the important part, brewing the beer.