I go to my parents grave site, which is next to my brother's grave and mow the grass, water the flowers, eat my lunch and take a nap in the TC. No one has ever bothered me. Very quiet and peaceful there and very dark at night. Yes I have overnight-ed here several times, without issues.
Worst comes to bare, I will show any inquiring souls my headstone and tell them I am just 'sampling' the environment, you know, just checking things out for this will be my resting place sooner than I wish!!!
Sometimes it is better to ask for forgiveness than ask for permission. I would not hesitate to overnight in any cemetery that is not posted against the act.
Lakeside