Mock Glue Up
Before applying glue and making a mistake we can't fix, I always do a mock glue up. With the pieces laying face down, I apply 2 pieces of tape long enough to span 3 of the 4 corners. I then flip everything over so the insides are facing up and put the top and bottom panels in the 1/4" grooves. Finally I bring the box together to see how things look. If you find your panels are a little to thick, you can take some sandpaper and lightly sand your grooves. My panels fit good so I moved on to applying some glue.

Applying The Glue
With everything looking good, I apply the glue to the miters using an acid brush. I keep the glue out of the grooves except for the very center of the bottom panel. Mine was a little loose and to prevent it from sliding, I put glue in the very center of the panel. And very little glue. 

Clamping The Box
With the glue applied I put the box together and applied some tape to the final corner of the box. You want to check all miters to make sure you don't have any gaps. I had 2 corners that had small gaps, but that was quickly resolved using 2 quick clamps in each direction. With the box glued up, I let it sit over night to dry.

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