Over many years I have seen that many campgrounds, whether National or State, may list a site for 30ft but when you see it it may look much longer.
What I have learned is unit length limitations are often more about being able to get the rig in the site. Earlier someone mentioned Yosemite as an example of a park with stricter, shorter limits and the biggest limitations there is the campground access roads. The older parks have some very narrow roads and the best backing trailer, 5th wheel and even MH drivers just can't squeeze into them without hitting boulders, trees, other camper's vehicles or something. Unless you pull into a National or State Park with a super gigantic rig, the policing of the length will be more about whether you can get in to the site you have reserved without damaging anything and if you remain fully within the site, both trailer and TV.
I think as many of these campgrounds are refurbished, and they do occasionally realigned them, they seem to be accommodating for these longer rigs. I have personally seen this.
