The 1/4" sides of the bulkheads needed a little coercion to come into uniform contact with the edges of the case. I set this up by placing a 2x4 vertically, clamping at the top and wedging it with a long fore-and-aft 2x4 at the bottom. Then, I forced pairs of wedges in the gap, squeezing the bulkhead sides against the edges of the case.