How do you get a library card when your address is a PMB

Below is a screen capture of the intersection of US17 (Orange Ave) and FL16 (Ferris Street). You will notice that the Green Cove Springs library is just west of that intersection between Ferris St and Bay Street. If you have your RV with you, you will most likely need to park in the small strip center on the east side of US 17 anchored by the Family Dollar. It's a short walk from there to the library.