You will need a very thick sleeping bag!
Pick your location carefully and you probably won't get any hassle. I've found motorhomes in a few of my favoured shooting venues before now, judging by the time and the lack of signs of life I rather doubt that they'd arrived that morning.
As for flying objects, that's part of the reason why my car has a rear strut brace. This is essentially an aluminium bar bolted across the tops of the rear spring mounts behind the back seats. It should do a pretty good job of stopping large or heavy cargo from demolishing the seats in a crash.