You really need to look at the places you want to stay at the most, and see if they have restrictions. As we went up in length from pop up to TT to 5er our options get less and less in many of our favorite places. It doesn't mean we cant get sites...just that we may need to reserve to ensure a site that suits our needs vs showing up first come first served. A truck camper is about the most flexible unit and a 40 ft fifth wheel will mean some sites are just not usable. If that's the length you want, then you will adapt and find places you fit.
Daryll