How do I get a p for a rental car to get on base around 8 or 9pm?

I'm going to my husband's AIT graduation in Fort Knox on August 26th but my flight doesn't land until 7:45pm so I wouldn't get to Knox until around 9pm. Is there an office located off base that late at night to get a p? I'm staying at a lodge on base and want to make sure I'll be able to get on base that night. I would think that there is someone always manning that off-base office but I'm not sure.