I'm trying to figure out travel logistics for an upcoming Sierra trip. I'm hoping someone can help me figure out if my plan will work.

I'm hoping to be at the Onion Valley trailhead by mid afternoon on 8/5, and eventually make my way up to Reds Meadow, then hike back to my car.
So far, I've been thinking about hitching from Onion Valley to Independence, taking CREST to Mammoth, and then taking the Reds shuttle. The problem is getting from OV to Independence to make the 6:30AM Saturday morning 8/6 bus. I could try to get down to Independence the night before, but I'd rather not pay for a hotel, and I hear it's harder to hitch in the late afternoon hours.
Any ideas? Will I have to wait until Monday until the busses run more often? My other option would be to park in Mammoth, and do the shuttle at the end, but I'd rather have my car when I'm done. Is the OV TH safe to park for 10 days? Or maybe there is another idea that I'm missing?
Edit: Oh, and I'm dead set on traveling south.

Thanks!
CM