We travel year round, and we do make reservations for high occupancy popular parks such as the state parks in Florida during the winter. We make most of those reservations 11 months out while we're there the previous winter. Other than that, we only make advanced reservations for busy holidays and when we have specific site preferences at a park that lets us choose. The rest of our travels are pretty much on the fly, with reservations made at most a day ahead, and often just an hour or so ahead, to insure we have a spot for the night.