Personal safety on the road and in camp.
Primary - avoid, leave. I can sleep any remotely level place my truck can stop. Airhorns to summon help if available. Cell phone, and good locks. Good escape route for truck and trailer to leave boondock site. Leave material goods behind, all "stuff" can be replaced.

Trailer security when I have the truck separate from the trailer
1. Chaining one or both wheels to the frame and axle with a good strong lock.
2. A trailer hitch ball lock that uses high quality round keys to release - Camper World has these.
3. Good deadbold on the door.
4. Park near other sundogs and meet them.
5. Remote sensing and tranmission - break in silent alarm that phones your cell phone.
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Have a planned exit route before parking. Don't get trapped alone. Certainly the most important is noise and communication. Next in importance is not being totally alone. That is in conflict with the desire to be alone, so this one is a problem. Each person must decide on issues of safety of course. In truth none of us are really ever safe if we had a standard of safety that said ZERO risk. Even at home there is no ZERO risk state. So the question is really more about feeling safe. For most people, the longer they boondock, the safer they feel to do it. It's what you become comfortable with. .