We saw a large RV in the parking lot behind the Cracker Barrel Restaurant in Kingsland, GA while on vacation recently. It was early AM, the curtains were closed, their "toad" attached, so it was obvious they'd spent the night. When I asked the manager about the company policy, he said Cracker Barrel doesn't mind if RVs spend the night, but they do like it if you come in for breakfast in the morning. Just park somewhere out of the way, like in the back or side. Some CBs have dedicated RV parking areas. He even gave me a map with the locations of all the CB Restaurants in the US on it.
The RV couple was inside having their breakfast when we were there, and they made a special point of looking the manager up and letting him know how much they appreciated spending the night. Not a bad idea, I'd say.
I would like to stress that I have not tried this myself. I'd probably check with the manager before I assumed it was OK to spend the night. The couple we saw may also have done that too.