I did this quite a few years ago, near a public beach not to far from my home. We went on a rainy day. The cave is pretty short (height wise) but deep enough to get in well out of sight. We put a dark blue plastic tarp up several feet into the cave, held in place with bits of dead tree branches, just in case anyone looked in, so they wouldn’t see anything. We cleared a place on the ground, and layed down a blanket, and went at it. It was pretty exciting being out in a state park, but with it being a rainy day, there really wasn’t much chance of anyone happening upon us.