In reply to Frank the Husky:
I've slept in the car in France in m'way Aires, service areas, and on country roads. Aires have always felt pretty exposed and on the basis of the stories on here I'll probably not do so again.
Well-lit service areas feel safer, and with some thought the bright lights can be escaped whilst also maintaining some safety. Police cars keep an eye on these areas, too.
When bivvying off country roads, I take care not to be visible. I was once kipping in my bivi bag in a field in Normandy and was awoken by a blood curdling scream from my friend (who had soloed the Shroud a couple of weeks earlier). "It's a snake! There's a snake!" I turned on my head-torch and shone it in his direction. The ground was heaving with large, red, and very slimey slugs. Hard men that we are, we retreated to the security of a tent.