<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by sohu:
Do you have to fly Southwest to get the credit. I mean do they require some proof of travel on Southwest within certain period of the rental?</font>
No, they don't. I've currently got a car from Alamo while mine is getting a fender-bender repaired, and I'll get the double credit.
Some rental sites ask for flight info as an option, I assume so if you don't show up they can check to see if your flight is late.
JP