I don't know how this thread got started, but I've heard all I care to. I have been camping at the side of the road and in gas stations or Wallymarts or where ever for almost fifty years and still do. All this paranoia WOW. 
We have to assume we all have a modicum of survival instincts that serve us well - now, consider yourself to be some sex crazed nut out to do people in. Stop and think about opportunity - very few folk on the road that stop in rest areas, are overly endowed with cash or other negotiables, - Query - why would you stop in a rest area to do your thing? You have to have a vehicle to get there in the first place and (if they aren't stolen) will identify you. And lastly - it would be a complete idiot to come barging into an occupied van - not knowing what was behind curtain no., 3  :-)  Minor precautions are a must even if you are in the center of your home town. There are people out there that are bad - and of course a very few are dumb enough to seek out their victims in a rest area.
I will continue to camp where ever I feel that I want to. I refuse to let a very few nut jobs limit my choices - The ultimate of this sort of reasoning is to never leave home without an armed body guard. Life is for living and it is in session - are you present? 
Bud Yandell