If you need more credits, a Hertz rental, using the AirTran link
https://offer.hertz.com/offers/index...off_and_dc.jsp
will give you one credit, per qualified rental, instead of the standard 1/2 credit per rental. Sometimes, you can rent a vehicle locally, for a very inexpensive rate, especially from an HLE location (off airport).
You can also purchase credits, at a cost of $39 per credit.
If you have an Amex card with Membership Rewards,
Convert your Membership RewardsŪ points into A+ Rewards credits that are instantly redeemable. It takes only 1,500 Membership Rewards points for 1 A+ credit.
Other options for earning credits can be found at
http://www.aplusrewards.com/reward_partners.aspx