Thanks to you both for your suggestions. I followed Luis' and it works great. Now for the second part, which I can answer by experimentation but might be nice to mention here for posterity:
Most of my UI is a tab panel. Using Luis' advice, I've now got my UI to move my controls and fill the extra space by resizing the tab panel. However, this does not resize the contents of the tabs. So presumably, another set of splitters will be needed on the tab to move/resize its contents accordingly. And since each tab is its own panel, I can expect to need a pair of splitters for each tab. Correct me if I'm wrong.
Thanks a bunch!
Dave Casey