Find a municipal park in a small town along the way. You can either ask for permission from the local police. Sometimes they say yes sometimes no. Or, if you don't want to risk them saying no, wait until dusk and pitch your tent in an out of the way place in the park. If you are quiet and respectful and you don't appear to be a vagrant, chances are you'll be okay. County fairgrounds or other public property are also good options. You can also look for private campgrounds but it will cost you $20+.