Lockers will get you into more trouble where corners become valuable. Corners are much easier to install when the tub isn't breaking apart. The only thing attaching the rear quarter panels to the rear sill under the gate are a bunch of little spot welds.
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When you do the corners, they hopefully have you putting a nutsert though the quarter panel into the rear torque box, helping to clamp the assembly together.
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If you are feeling smart and are careful with layout, you get four nutserts into the torque box.
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