We have been travelling 10 seasons, averaging 150 nights a season, usually not travelling August but every month April to November. We have done all the major NPs like Yosemite, GC, Yellowstone, Glacier, Denali. Most of them multiple times.
Very seldom have reservations been made at any of these parks. The few times have been for dates spanning a holiday weekend. Yes, you have to play the game a bit. At a high demand CG get there on Thursday. At a not so high demand area get there early on Friday for the weekend. Except for the really high demand parks like Yosemite Sunday to Thursday is usually no problem without reservations.
There is a trick to that too. Don't be so demanding. Be prepared to dry camp if necessary. A dry site is better than no site at all.
I wonder if the problem is not so much the lack of sites but the lack of sites with the trimmings like W/E minimum?
We rolled into Bay Bridge CG in Yellowstone NP one afternoon, mid week, mid July, NO reservations. We squeezed our 34' plus truck selves into one of few sites possible that were left. By dark there were still a very few open sites left. Bay Bridge is dry camping, open but not groomed at all, so the bison tend to roam through. A whole lot better IMO than Fishing Bridge CG which is nothing more than carpark camping with utilities & always booked solid.
