The only time I had things stolen was years ago when I was parked temporarily at a customer's industrial facility in Gardena, CA. I had a motorhome at the time and it was situated within a fenced area. Somebody drove their vehicle into the fence gate one evening while I was away, knocking down the gate in the process. They then proceeded to force their way into my RV and stole lots of stuff. In retrospect it was really my fault for parking my RV in such a high crime area, notwithstanding the fact it was fenced in.
Since that fiasco I've always stayed at commercial RV parks and have never had anything stolen. The only item I leave outside besides lawn chairs is my bicycle, which is chained to one of the landing jacks with a Kryptonite chain and lock. Sure, someone with a large bolt cutter may be able to break it but in an RV park I think that's a remote possibility. I bought the bike for $75 from a friend. If I had paid many hundreds or thousands of $$ I would probably store it inside my RV, which would certainly be a pain.