order comments

Greetings! How can I display uc_checkout_pane_comments in uc_cart.module on uc_order-customer.tpl.php? I wanted to include it to display in my invoice form. I replaced the word "Order comments" into "Due Date". "Due Date" somehow is displayed in the invoice form but not the value uc_checkout_pane_comments. Thank you so much in advance for your help.