You are right about the Scrolled Pane working better than the Scrolled Frame. Actually, the thing you probably want to do is put a Frame (packed so that it expands and fills) into a Scrolled Pane. The Scrolled Pane should take care of adjusting it's scrollbars to the new frame size, as you add widgets to the frame.

#!/usr/bin/perl
use warnings;
use strict;
use Tk;
use Tk::Pane;

my $count = 10;
my $Frame;
my $mw   = tkinit;
my $pane =
  $mw->Scrolled( 'Pane', -scrollbars => 'e', )
  ->pack( -expand => 1, -fill => 'both' );
$mw->Button(
    -text    => 'Refresh',
    -command => \&Refresh,
)->pack;
Refresh();
MainLoop;

sub Refresh {
    my @a;
   $count +=10;
    for ( my $i = 0 ; $i < $count ; $i++ ) { push( @a, int( rand(100) 
+) ) }
    DisplayCheckButtons( $pane, @a );
}

sub DisplayCheckButtons {
    my ( $parent, @names ) = @_;
    $Frame->destroy if $Frame;
    $Frame = $parent->Frame->pack( -expand => 1, -fill => 'both' );
    map { $Frame->Checkbutton( -text => $_ )->pack } @names;
}
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