A dehumidifier pulls water out of the air and stores it, so the first job is emptying that tank. Most models also have a compressor, which means the same upright handling and rest time rules that apply to a refrigerator apply here too.
Pro tip: Run the unit empty for a bit or leave the tank out to air-dry before storage to prevent mildew.
Watch out: Empty the water tank before moving, or it will leak throughout the vehicle.