Phil,
College Park (KCGS) is located in DC Flight Restricted zone which has special entrance requirements in addition to what's required to fly within the DC SFRA. Also I'm pretty sure you can't do Customs there.
Here's the link to learn all about the SFRA and the FRZ:
https://www.faasafety.gov/gslac/ALC/course_content.aspx?cID=405&sID=640&preview=true
What is the FRZ, and Where is it? The Washington DC Flight Restricted Zone (FRZ) is within, and part of, the SFRA, but this area is subject to additional security requirements and procedures. Unlike the SFRA boundary, which is a ring established on a 30 nm radius from the DCA VOR/DME, the FRZ has a unique and irregular boundary.
How Do I Fly VFR in the FRZ? VFR operations in the FRZ are extremely limited. Flight operations under parts 91, 101, 103, 105, 125, 133, and 137 are prohibited in the FRZ without a waiver. VFR pilots should think of the FRZ as a “no-fly” area. The only exception is for the Maryland 3 airports: College Park Airport, MD (CGS), Potomac Airfield, MD (VKX), and Washington Executive/Hyde Field Airport, MD (W32)
To operate to or from College Park, Potomac, or Hyde, aircraft, crew and passengers must comply with security rules issued by the TSA. Pilot must be approved (vetted) and receive a personal identification number (PIN) for use in filing a FRZ flight plan. Before departing, the pilot must call the Washington Hub Flight Service Station (FSS) to file an IFR or FRZ flight plan for each operation, whether or not the aircraft makes an intermediate stop. The pilot must provide the assigned pilot identification code, and the Washington Hub FSS will accept the flight plan only after verifying the code. For information on obtaining a pilot PIN, please see the TSA website.