EC (Emerald Club) is Nationals frequent renter club and EA is Emerald Isle which is a benefit of EC. At certain airports, MCO being one of them, you can reserve an intermediate class car, bypass the counter and pick any car in the Emerald Isle and process the paperwork at the exit booth.
With luck, you may get a free upgrade using this process, you will eliminate hassles (mainly the insurance hassle) and get on your vacation much quicker.
I have found this service to be a great conveinence and with the right codes, a money saver.