Jon,
After looking real close at my panel, it doesn't have the same style bracket as yours. Mine has a steel lip (flat channel) on the two sides and bottom that seems to be be part of the box and is screwed to the bulkhead. It doesn't appear to be a bracket. The box has been tack welded to the bulkhead at the top.
What am I missing? Could mine be better than yours....
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Right side
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Box is tack welded in the dark area below the obvious two spot welds
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Left bottom side