Has Anyone ever been turned away for Length Restriction?

If I am reading the OP's post right, I think that some are missing the point of the OP's post.

Have you been turned away because you were less than 30'?

I have seen several ads from Motor Coach Resorts that have a 30' minimum.
Doesn't bother me because I am not staying there.

My truck and trailer is 59.5 feet long from hitch to the tip of the cargo carrier overhanging the trailer bumper. My trailer is 35.5 feet and with the cargo carrier, a total of 38 feet.

We pick our campsites based on the size of the trailer. (we always use 35 feet). We've never encountered a campground that could not accommodate us. Of course, we made reservations and pick our own spots. If traveling and we need an over-nighter, we will find a campground on the internet (phones), and call ahead for (1) Space available, and (2) Length, and if traveling (3) a pull-through site.

Our first camper was 24 feet total length. Our second camper was 31 feet total length. Our third camper is 35.5 feet (without the carrier), and we've never had problems finding a spot in any campground, unless the campground was already 100 percent already filled. We have encountered that.

Never in over 50 yrs of towing RVs

If it fits the site AND YOU ARE NOT A PIA then you are good to go.

Our rig is just shy of 33' and I have never been turned away whether it's a private or state/federal campground. Depending on the size of site available I've squeezed into sites that were intended for smaller rigs as well as taken larger sites intended for larger rigs. We've always arrived and just paid and parked into the designated site.