I vote for rest areas. I am the son of a long haul trucker and the sound of idling diesel engines is just white noise to me. I think that paying $40 for a six hour stay in a campground is a waste of money. There has been many a night when I have rested in a rest area or travel center parking lot. Flying J even has RV parking and they don't mind if you park there for a few hours. It's a lot like Walmart not minding if you park in their lot, they know you may come in for supplies, or eat in their restaurant.
