I have made 10 cross country trips so far and I did not have reservations on these trips except if I will be traveling during a holiday weekend. My last trip was 53 days and we had reservations in Helena Montana for Labor Day weekend but after I arrived even then there was plenty of open spaces. We had reservations at Dos Picos County Park in Ramona Cal. because it is very popular on weekends and is often full. We have even camped in Yellowstone at Fishing Bridge without reservations. Just be flexible and you should be fine
