Often, nobody will bother you if you pitch a small tent in a highway rest area. If there are no bugs out, you can even just roll out your sleeping bag on a picnic table, it's no different from anyone parking their car to sleep. I've also devised a way to set up my tent as a more inconspicuous bivy sack when there are lots of mosquitoes.
A couple of times when I was dead tired and caught up in a built up area without options, I searched for truck stops and camped behind where trucks art parked. It can be a noisy affair, but truck stops usually have conveniences like showers and late night food. Sometimes those odd experiences make for weird memorable moments.