Hello and welcome to the RTA forums !

You can't pull up anywhere in an RV, so yes RV parks would be the normal, although truck stops and occasionally large stores like Walmart allow an overnight, but only when the manager has used there discretion and given you permission. These options would be for getting some sleep only, not setting up camp and getting the BBQ out.

You don't have to book in advance for campgrounds, but in the summer Months you will find popular tourist places such as National parks book up early, and you might have to hunt around for places nearby. It really depends on if you want the freedom to keep an open book or the security of knowing where you will be staying the night.

You will find lots of RV info by clicking the link in the tool bar, near to the top of the page.