Well I was just mentioning the car parking thing because while en route to hiking the Percy's recently, I think I saw a sign on the Nash Stream road that said something to the effect of, "No overnight parking." Maybe I'm wrong.
Which led me to believe you may have to be on an extended backpack (Coos Trail) to camp at Percy Loop, be willing to hike in from the Christine Lake area or elsewhere, or be dropped off/picked up.
BTW, I went by the Percy Loop campsite on the way down. One tent platform that could fit two-two person tents. And a bit of room on the ground for a couple more tents. The water source stream was flowing well two weeks ago.