Large gravel lot behind Cal-Cheak campground. Stayed for one night along with a handful of other campers. Police drove through in the morning but didn't bother anyone. The campsite is $12/night self registration. I've heard you can stay in the gravel lot and still access the campground facilities for $6/night. I didn't personally verify this though. There was one ugly looking old motorhome that looks like it's been there a while.