No, I just used the OOAG code. I just went to Dollar and tried it again and got the same price again, $268.68. But, then I read your post again and then tried using the BNA airport code and the price was $457. If you are trying to use these codes for a rental in Nashville it won't work, they are only good for rental in Florida.
We aren't sure if we are flying or driving yet (my parents are flying from Detroit). The best deal from Nashville I found for a minivan rental was through Hertz. Renting locally from Murfreesboro, with a $35 off a weekly rental coupon and a discount code, the rental is $402

. Not unlimited mileage either, so I'm still looking and hoping as our trip gets closer the prices will go down in case we don't fly and have to drive.