If you book a room in advance and find that you want to cancel, is there a cancellation fee? How early do you have to cancel to avoid a fee? This varies from place to place, but that is an important question.
Are you going to be traveling during peak travel season or not? In other words what is the likelihood that rooms will be available on short notice if you do not make a reservation?
I have not credit card toured, but I have toured enough that I have figured out that often you want to have a reservation in advance, but sometimes was not really needed. And my first question always is f I cancel, what does it cost me and how far in advance do I have to cancel. I usually camp when touring, but I often mix it up with some hostel stays, and I usually make reservations at the hostels but almost never make reservations at campgrounds.
I have toured in some areas where you are out in the open exposed to the wind and the wind can determine whether or not you can travel each day. But fortunately, GAP and C&O is mostly well sheltered in the trees, thus you should not have to take a day off due to weather, provided that you are able to travel on wet rainy days. Being a six day trip, it sounds like it has to be a six day trip so you can get back to work or make other critical appointments. Thus, I think it unlikely that you would want to cancel a motel on any particular day because you are making short distance that day. I say it is unlikley because if you did, the next day you would have to make that up since your six day trip probably has to be a six day trip, not seven.
Bottom line, sounds to me like if you cancel, you would cancel the whole trip well in advance, not one night.
Side note - I did GAP and C&O so many years ago that I do not know if the hostel in Rockwood is still in operation, but if it is, I do not recall if they provide bedding, towels, etc. If you plan to stay there, make sure you know what you need to bring.
Photo, we had several consecutive days of rain when we did GAP and C&O. Hopefully, your trip will be drier.
