As noted, mid-August is still Tourist Season. There's a bit of a sweet spot from (maybe) the last week of August to the middle of September. Anytime after 1-September, there's an increasing risk that facilities will be shut down, but it's just about a certainty after 15-September.
FWIW, there's lots of places to boondock and places to get water and dump sewer that are available until freezeup, just not most of the standard camping facilities. September is one of the better months to be in Alaska IMNSHO. Bugs are gone, tourists are gone or rapidly disappearing, scenery is spectacular, etc.