Not sure if this would help you out or not...
I am taking my son camping that weekend. We are arriving at the Portal campground on Aug 29th in the early evening. We are leaving Santa Clarita around 2pm that afternoon. Depending upon traffic, I would be up there around 5 to 6. I'd probably have enough room to bring up your stuff. It might be later than you'd like or need your stuff... If that would help you out, let me know.