Custom form with edit regions

Here's the problem:
I have several simple forms that all roughly follow the same layout
and pattern.
I thought it would be easy to create a paren BaseForm class with the
basic layout that is common to them all (buttons positions, common
validation code) and also with an edit region that would be filled in
in the subclasses. I can't seem to find a way to make the Panel in the
parent class editable in the UI designer for subclasses. Not sure
where to begin with the UI Designer stuff... Any tips?
TIA.