We find there are private campgrounds/RV Resorts near the popular and many other national and state parks. We have a 38 foot 5th wheel and have always been able to find a site in the areas where we visit. Sometimes it's a public campground and most of the time it's a private resort because we like to enjoy the extra amenities.
During the week it's easier to get a site. For weekends and holiday weeks, with planning you will be able to find a site in or near most destinations. Go for the longer RV and you'll not regret it.
