Turns out Onion/Grays/Horseshoe are ~14 miles away AS THE CROW FLIES, which means 35+ miles driving. Ugh, that means getting up an extra hour early to make our 3am trailhead start.
I'm considering doing this: reserve (i.e., pay $16 for) Onion/Grays campsite as a back-up plan, then hope to snag a walk-in at the WP Trailhead or the WP Family Campground. My hiking partner is a photographer and wants to do some shooting north of the area on Thursday. That probably means getting to the walk-ins much later than noon. We're going to call the ranger to get their opinion of getting a walk-in late in the day August 9th.
Anyone care to take a guess at the likelihood of snagging a walk-in at WPT or WPFC at 4pm on a Thursday August 9th timeframe?
I like that, 3am bear alarm clock... just add food

You'll be all raring to go at the trailhead with that adrenalin rush