Membership campgrounds for members only. The advantages to membership campgrounds are they are almost always attractive and secure parks with plenty of activities and member interaction. Only in the busy summer months, especially on holidays when spaces in popular campgrounds are almost impossible to find without a reservation. National Forest campgrounds are often the last to fill. While they offer few amenities, their settings in forests, often by lakes and streams, can be peaceful and scenic.
Reservations are a good idea at private campgrounds especially in the prime seasons and on holidays.
A few are still free, but not many. The rates at some campgrounds, though, like KOA, are based on two campers per site. An additional charge of a dollar or two per extra camper may be charged. I camp a lot. Two ways come to mind.