You can sleep overnight at a rest area along the road or interstate but be aware that it can be unsafe because of potential robberies etc.
A cop may also come by and ask you to leave for safety reasons in some places as some Rest Stops don't want you staying overnight due to safety concerns.
Most Home Depots and some Walmart stores will allow you to park your RV overnight and sleep without problems which would be a much safer option instead of a way out rest area with less security.
There have been a few people murdered at rest areas along the interstate overnight so I would advise against staying at a rest stop.