Nothing is safe from a sufficiently motivated thief. At best, you can make your stuff harder to get than someone else's. If I'm a thief:
I'll steal a bike or anything else that's portable without a lock.
I'll steal stuff from an unlocked RV or toad.
I'll steal stuff from a TT or 5er with no tow vehicle around.
I'll steal at CGs with multiple entrances/exits before one with a single entrance/exit.
I'll steal at a CG that doesn't have an office at the entrance, or has a "Closed" sign at night.
I'll steal at a CG that has sites that are widely distributed and separated by trees.
And I'll avoid any RV that has a very heavy chain attached and a dog dish with "Killer" written on it.