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I haven't tried this, but what about adding the Box component to the Swing or Layout palette in the default component palette configuration?
This could be done, but probably with some additional work - at least as Box is not JComponent, and cannot have layout changed. I don't see having Box in palette too urgent - using JPanel with BoxLayout is almost equivalent.
*** This issue has been marked as a duplicate of 8304 ***
Resolved for 3.3.x or earlier, no new info since then -> closing.