I've never had an issue, ever.
One state park we stay in says it has a 28' max length, our 39'er fits great. Yes I did stop and physically look at the site before we made our reservations and discussed it with the boss at the park. Seems it's a typo on-line, that has yet to be corrected.
On the opposite side of that, about 10-12 years ago we had July 4th holiday reservations at a private park in Old Forge, NY. We made the reservations in January as being the holiday things filled up quickly and the park always sold out.
When we arrived the girl who checked us in offhandedly said "I hope your camper isn't very big". Obviously I was a little miffed. When I asked her how big the site was she said 30'. When I told her we had made our reservations in January and clearly said we had a 40' MH, she said "go check out the site and if it's not big enough we'll see what we can do". I'm not sure what she was thinking as again, they were sold out.
With the help of great neighbors moving all of their vehicles I was able to maneuver the MH into the site, with not an inch to spare. We haven't been back since.
So...if I found a MH I liked I wouldn't let a 34' length sway my purchase even a little. For the one park you may ever miss you'll enjoy the extra room every time you use it.
