We make reservations. It very much depends on where you are going and when and in what part of the country you are in. Here on the East Coast in popular areas it can be hard to find a vacancy during peak travel times and that can be Spring, Summer, and Fall and that does not include holidays which are booked a year in advance. We have had situations where we have had to change travel plans close to departure and have not been able to get a reservation. It is all a matter of preference. I want to relax when traveling and not be concerned that we won't find a site. Others don't care - that's not me (yet).