perhaps you are using GridBaggy the wrong way? dunno what the correct way is but i usually use GB for the main big layout and add panels here and there.
Perhaps I should give it another chance. Your approach is good, and I have tried that before, but found I still ended up with hard-to-maintain code. If you know it well enough to use it quickly and easily, then I can see it kind of solves your problems; it certainly has enough flexibility to ... but you still have to do a lot of work that should be unnecessary in a modern GUI API.
i haven't tried a GUI tool in Java yet.. it's on my 20 km long todo-list though.
Good ones are excellent, and I've found they can make up for the deficiences in e.g GBL, by making the process of creation and editing simple and easy.
But the only free one I'm aware of that works is the Forte/"One"/netbeans one - and running that behemoth is more than my patience and sanity can tolerate these days.
If someone knows of a free one somewhere else, that can work on live code, automatically ONLY altering the GUI parts of the source class? I'd be very interested to see it...