a question about the cart(adding coupons)

ok so im looking to buy some locos from jointed rail and i saw that i still had the coupons from the survey
i wanted to know if it was possible to add more than one coupon and how do i do it

I haven't even seen a slot to add any coupon at all, much less multiple...
I, too, am curious of this...

The area to enter a coupon would be under your cart in the My Cart area and only one coupon code may be used per order.