Collapse checkout pane by default

I tried the following:

function uc_coupon_collapsed_form_alter(&$form, &$form_state, $form_id){
  if ($form_id == 'uc_cart_checkout_form') {
  // Collapse 'coupon' fieldset.
    $form['coupon']['#collapsed'] = TRUE;
  }
//  drupal_set_message("Form ID is : " . $form_id);
//  drupal_set_message("Forms: " . print_r($form,true));
}

Doesn't work. Then I read this. So simply overriding is not possible.

I also tried this but the code doesn't work and I could not find the right one. Any more ideas?

I also tried to change the module by adding 'collapsed' => TRUE which didn't work either:

function uc_coupon_cart_pane($items) {
  $panes[] = array(
    'id' => 'coupon',
    'body' => drupal_get_form('uc_cart_pane_coupon'),
    'title' => t('Coupon discount'),
    'desc' => t('Allows shoppers to use a coupon during checkout for order discounts.'),
    'weight' => 1,
    'enabled' => TRUE,
    'collapsed' => TRUE,
  );
  return $panes;
}

Thanks a lot!

To save others some time I attach here the module.

Cool!