As campground hosts in both state and national parks, we are aware that this is an issue. It's tough to explain to a 40-foot motorhome owner that someone with a backpacking tent or 16-foot Casita took the last site the big rig could squeeze into. Still, in a first-come, first-served campground, there is little we can do. If someone asks us for site recommendations, we offer size-appropriate suggestions, but the decision is left to the park visitor. If the small rig chooses a big site, it's OK with us (although we may frown when we walk by).