You can test each of the manufacturers_id with:
$chk_manufactuer_10 = $_SESSION['cart']->in_cart_check('manufacturers_id','10');
$chk_manufactuer_25 = $_SESSION['cart']->in_cart_check('manufacturers_id','25');
Now you can add to the cost based on these results by added the extra cost to:
Code:
$this->quotes = array('id' => $this->code,
'module' => MODULE_SHIPPING_PERWEIGHTUNIT_TEXT_TITLE,
'methods' => array(array('id' => $this->code,
'title' => MODULE_SHIPPING_PERWEIGHTUNIT_TEXT_WAY,
'cost' => MODULE_SHIPPING_PERWEIGHTUNIT_COST * ($total_weight_units * $shipping_num_boxes) +
(MODULE_SHIPPING_PERWEIGHTUNIT_HANDLING_METHOD == 'Box' ? MODULE_SHIPPING_PERWEIGHTUNIT_HANDLING * $shipping_num_boxes : MODULE_SHIPPING_PERWEIGHTUNIT_HANDLING) ) ));