I found my mistake, a very basic one.
I was using
VTKscene = QVTKRenderWindowInteractor(self)
but should have been using
VTKscene = QVTKRenderWindowInteractor(page_VTK)
where page_VTK is the widget I created to display the scene.
I apologize for cluttering up the mailing list with my ignorant questions.
Gib