in four years we've traveled over 25,000 miles, been on the road close to 300 days. We do make reservations at major destinations where camping spots may be full or an issue and we plan on staying several days or weeks. However, on the road, looking for an overnight spot we have never made a reservation. for an overnight stay it's been easy to find a spot good enough for the night. Many spots we have found in small towns, remote areas have been beautiful and we put them on our future stop list.
the nice thing with this is we aren't tied into a specific distance each day. some days we find things to do and don't travel very far, other days, longer.
Besides the obvious campgrounds, many small town county seats with a fairground have the fairground open all year for overnights, many times we and others have pulled into small towns, found a nice restaurant with a big lot, go in say we are hungry, and can we park the trailer overnight?? Never been turned down . Small town churches also are another option. And if you are an elks member, many elks clubs have campsites as well. Then there is the wallmart etc. And in some states they allow up to 12 hours in a rest area. we've done that, we don't put out the slides, don't put out the generator etc. go for an evening walk then hit the trailer.
also many smaller off the main road truck stops/gas stops have an overnight free camping area as do many tourist attractions/stores etc.
We tend to avoid interstates, don't really save us any time and we prefer the scenery of backroads anyway. We don't go any faster on the interstate than on secondary roads anyway. 60 or so on both.