If the site is being vacated the day you check out, then you might get it. If the Fort is full or close to it, they will not leave the site unoccupied for a day or two just so it will be available for you. You are much better off requesting the things you like about the site rather than the site itself. For example, if you like the site because it is near a comfort station, then request that, if you like it because it is to the back of the loop and is quieter request that. The problem with asking for a specific site is that the assigners really don't know why you wanted that site and if it is not available they really don't know what you might find as a comparable site.