And yes, the online reservation systems are a pain to work with until you learn how they work. One thing to remember is that many of them will post campsites as "not available" during the closed season, but if you change the date of your trip to when the season opens the sites will become available. To me, it would be more logical to state "season closed" when the season is, well, closed.
Also, feel free to ask about campgrounds in these forums. I've gotten great advice and ideas for our camping trips from Open Roads!