You might want to use Tk::Adjuster...

...
    $textbox = $mw->Scrolled(
        'ROText',
        -font       => "{Courier New} 12 bold",
        -background => 'DarkBlue',
        -foreground => 'OldLace',
        -scrollbars => 'se',
        -wrap       => 'none',
        -height     => 8
    );
    my $adj  = $mw->Adjuster( -widget => $textbox, -side => 'bottom');
    $adj->pack( -side => 'top', -fill => 'x');
    $textbox->pack( -expand => 0, -fill => 'x', -anchor => 'n' );

    my $buttonFrame =
      $mw->Frame()->pack( -side => 'bottom', -fill => 'both', -expand 
+=> 0 );
...
[download]

...which allows you to adjust the textbox size with the mouse.

The Scrolled widget is a compound widget, and the ROText widget can be retreived via $textbox->Subwidget('scrolled'). Changing its size and repacking it just changes the size of the text pane, not the entire Scrolled widget (scrollbars, corners and outer frame). I've tried various ways of packForget and pack on them, to no avail.

But the Adjuster just does the job ;-)