Hi, I would give it to them when you get there, but my hunch is one coupon per rental....just do the math on which one saves most or if the car up grade is that important
HINT....Emerald Isle service is so slick at National. You bypass the counter and go right to long isle with 30 to 50 cars and you pick which one you want. In Orlando there are frequently small SUV's Rendevous, mid size on the "Emerald Isle." You can join for free. I think you can just call them and say that you love National and would love to have Emerald Isle. They may wave the $50 fee for you...
Ted