🚀 go-pugleaf

We are working with InterViews 3.1 and Unidraw.
I have an Editor with a big Viewer, 2 scroll bars and a zoomer in it.
I need a panner that will have a transparent thumb and a copy of the big viewer
under it. (this way the user can see which part of the big Viewer is visible).
My approach was to construct a transparent panner made of an XYSlider and a 
amall Unidraw Viewer.
I created to classes, a transparent panner, and a small Viewer.
When I put them one next to the other (in an hbox) both of them
work: The panner moves the picture and updates the size of the thumb on 
zooming, and the small viewer is updated by the editor following a change in
the big viewer.
However, when I put them one on top of the other (using overlay), the
panner is not visible (although it moves the picture).

Is my approach correct?
Can I put a glyph over an interactor in an overlay?
If not, how do I approach this problem?
I will appreciate any suggestions.
Any example that has any relation to this problem will be great.


Thanks:
Abshalom Aviv