I've thought about using other geometry managers, though I'm rather attached to Form.

I would go with this route. Form is probably the least frequently used geometry manager in Perl/Tk, and thus might contain bugs that have never been earthed before. This is the first time I see a question on form, and I have been a regular on comp.lang.perl.tk for many years.

Maybe Form's springs would help?

Perhaps, but I don't think so. The docs of form have this caveat: 

BUGS

Springs have not been fully implemented yet.

[download]
I would go with pack or grid.

In reply to Re: Tk container size question by qumsieh
in thread Tk container size question by foxcorner

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