Black bears can usually be scared away by loud noises.
Open the window of your trailer or motorhome and yell at them, or bang some pots together and they will normally take off. A barking dog will usually do the trick as well. However, if they have become accustomed to people and getting food, it might not work for long.
Troublewaters has it correct. If a bear is around he's looking for food. No food or food odors - they won't stick around long.