We've been to nearly every NP in the west, and probably half in the east. We've never had a problem getting a site. We often get one or two nights, and move, but we always find some spot for the night.
We haul a Truck Camper and are 22 feet, so that helps. Sometimes, we end up in a national forest for a few nights near a major NP, but we always get in and stay as long as we want (based on days allowed).
That might not suit a large RV, a larger family, or foreign visitors. But our first priority should always be "protect our wilderness, our watershed, and our wildlife." If we fail in that responsibility, additional campgrounds will be the least of our problems.
