Rivnuts from Homestead,PA on 3/19/2022 3:50:22 PM:
If you are referring to Mile Marker 0 of the GAP in Cumberland, I would recommend the YMCA there. It’s maybe a mile away from Canal Place in Cumberland where the GAP mile markers begin counting. It’s a pay-for-stay site but you have access to the YMCA facilities, notably the showers, and there is a small covered pavilion if you encounter inclement weather there.
If you are referring to Milepost 0 of the C&O in Washington, i am not aware of any campsites nearby. The last camp site on the C&O approaching DC is at Swain’s Lock which is around 17 miles from Milepost 0.
Perhaps someone local to DC can offer additional insight into camping areas around DC.
I hope this answers your question.