Hey Gary
I agree that there are mucho many more car campers this year. The FS spot I'm at now has told me they have significantly more tent campers this year than normal. The last RV park I was at did not allow tent camping - a nice gesture towards their RV bread and butter clientele. The Cooke City FS camp I was at only allowed "hard-sided" camping - I guess a guy got eaten 10 years ago after being pulled from his tent by an emaciated grizzly bear.
Since May, when I was at a State Park in Cottonwood, AZ, the reports from camp hosts and rangers has been that everything fills up every nite. Even then, RVers were camping in one site, and then had to move each day to another site to get a longer stay. Only place I know of that didn't fill was Helper, UT at Castle Gate RV Park. But, I haven't been to truly "boonie" spots - been in Winslow (SP), Flagstaff, Cortez, Moab, Vernal, Cody, Cooke City, Gardiner, MT and now West Yellowstone. More than that, I have spent hours and hours on recreation.gov planning a route and looking for spots to reserve. The Forest Service has added lots of campgrounds to the reservation system. Everything is reserved - much more than usual which I take as another indication of lots of folks out and about. I have reservations everywhere up through Sept. 17 - and will be adding another week onto that soon as I think I'll visit the folks I met in Las Vegas last spring. From October 1 through Jan. 15 2021, I also have reservations.
I'm still chicken when it comes to heading for truly boonie spots -- like many of those on Campendium. Plus my travels are still taking me to parks, and attractions, rather than just camping/staying somewhere in the rig. I wish I could be of more help and recommend some great places for you. Alas, I cannot. I do hope your prediction of less crowding in September comes to fruition.
Linda