I already have a great rate using the Visa Magic code. When I tried it today it had gone up--you won't believe this--by over $1000!!!!!!!!!!!! So now I am worried about using --87. My dates are Dec. 28 - Jan. 6 and Alamo's rates are also out of sight. I do belong to AARP, but no rates can match the $274 I have with --87 ($1315 today!!!) and $196 I have with --67. So is --87 safe?
I think if you've already booked it, that's a start-you have a good rate locked in. Keep an eye on the boards and see what folks' experience is at the counter. I think it's a very good sign it was advertised at Moussavers. You can always book a backup, as long as you cancel within the rules. I sometimes have two National reservations for the exact same time until I figure out which I'm going to use. I never keep both, though. I always cancel one. That Visa Magic Code rate didn't include a second driver, and National wouldn't let me add our Emerald club # so we would have been charged for a second driver. The free spouse (second driver) is a great benefit of AARP bookings.
Don't quit checking AARP, by the way. Their rates can really vary, especially as you get closer. They can really go down.

We are transporting some family members with mobility issues, so we really need a specific size vehicle. I'm a happy camper, now!

Good luck! Sometimes I think booking rental cars is like looking for the Holy Grail!
