There is a guy near one of the entrances that allows trailer parking on his land for a donation. He's just a few houses up from the house with all the solar panels, for anyone who has been there. I'll try to find his name.
We went last year and stayed at the hotel just down the street from AOP. Absolute blast. TONS of rocks and lots of water crossing. Some of the crossing can get deep, and people have tried to mark some areas to avoid where the bottom drops off (8ft+). Once on the trail, you're pretty much committed to going through. There are many side trails, but no real exits. At a leisure pace, a group of 6 of us took most of a day with stops for lunch, pictures, exploring caves, etc. Trails can get narrow, especially after a storm knocks over some trees. Bring a chainsaw just in case.
The trail is a public "road", but it is not maintained and probably hasn't changed much since wagons went down it. Look out for SXS and four wheelers. Also some cool Indian burial mounds throughout.