Originally Posted by wahooflyer

You don't have to book through the Carlson Web site to use the Carlson code. 5760339 works through nationalcar.com and I've never been challenged by any of the exit booth agents when renting with it.

The underage fee with Carlson is only $10 per day, which helps a lot for this 23-year-old!

I've started using some of those universities' codes mentioned above since they charge no underage fee, but those only work well for rentals returning at the same location. One-ways are charged per mile, which negates any cost savings in most cases.