It is the foolhardy traveler who fails to make reservations and instead depends on luck to find a place to stay after a long day of driving. Popular RV resorts in favorite tourist destinations fill up quickly, and reservations often need to be made many months ahead for stays during busy times.
Most RV parks require a deposit on reservations. While a credit card is usually the easiest way to guarantee a space, some campground owners may hold a spot with a check (don't forget to get it in the mail). Your credit card should not be charged until you actually check in, or only one night should be charged in case you have to cancel your trip at the last moment.
When you make reservations, ask about the campground's late arrival policy. No matter how well you plan, you may run into delays on the road or mechanical problems. If you are late, you will need to know how to get to your camping space with as little disturbance to other campers as possible.
If you own a large RV with multiple slideouts, you should make sure that the campground you are considering has RV sites that are wide enough to accommodate your rig comfortably. Get it in writing if possible, but at least get the name of the person you spoke with just in case.
Some public campgrounds do not take reservations for camping but work on a first-come, first-served basis. If they do make reservations, they may only have a limited number of sites for larger RVs, or, in many cases, they will not be able to accommodate them at all. Public campgrounds often do not have full hookups (or even any hookups). These are all things to consider and ask about when you call for reservations.