The bigger the motorhome the more limited your campground options are, there are even ones that my sub-30 foot coach will not fit into. The thing you will likely find is that it is not only the size of the rv site, but also the ability to thread your way through the winding access roads that limit your options.
There is also a question of the percentage of RV sites in any given campground that can accommodate that size coach, as well as the TOAD car you will likely be pulling behind it. An example that comes to mind is a Forest Service campground I stayed at a couple of times a couple of weeks apart last summer in Wyoming, 18 RV sites plus a few tent camping sites. Some of the sites would barely fit a 25 ft coach, most would probably fit a 30 ft, a few might fit a 35. When I was there the second time someone had a 40+ tag axle diesel pusher towing a Jeep shoehorned into a pull out space, how they made it around the loop to that point I don't know, but I can tell you to fit in there meant there opposing corner tires were dangling half off the pavement.