I have 1 concern: My permit for Whitney is on Sunday, July 31st--a weekend. I am afraid of the campground filling up at Horseshoe Meadows. What if it does??? Then what does a person do?
Can you get up there on Friday? Not only would the second night help your acclimation, it gives you a much better opportunity to grab a good site. There are actually two campgrounds there and the sites are first-come, first-served, with no reservations allowed. Combined with the high altitude, it's a rare thing that all the sites are gone.
Here's more info.
In the unlikely event you can't find a site at HM, sleeping in your vehicle at the Whitney Portal is regularly done by many. Not the best option, but better than sleeping at 3700 feet in Lone Pine. Recline the seat, snuggle into a bag, and do your best. I doubt if you'll have to resort to that, though. Get to HM on a Friday and you should be in good shape.
Remember also that with a dayhike you'll be getting that extra-early alpine start, so if you only stay the night prior to your hike, you're really not getting a full night of acclimation. If you could get to HM on Friday, sleep a night there, ramble around at elevation for a day, then get a few more hours sleep before rising at 1:00 or 2:00 am on Sunday the 31st, you'll be in eminently better shape for 14,500 feet.
