Calakmul

When we were in the area, January 2006, camping was not allowed at Calakmul Ruins (at least not officially) and you do not need a guide to visit. The biosphere may be different. I would not categorize camping at an archaeological zone or ruin site as dangerous, at least no more so than camping at an equivalent in the states. My advise would be to talk to the attendant at the gate and simply ask if it is okay to "pasar la noche aqui". If yes, leave a tip and don't leave a mess. We were told that camping was permitted at Kohunlich, closer to Chetumal.