When I see campsites that say "no trailers over 30 feet", are they referring to the actual length, or the nominal length?
Your not going to like this answer...
It depends on who is measuring and measuring what. Many times campsite will say no trailers over (fill in a number) but when you actually get to the site there is a ton of room because you can back over the end of camping spot until rear tires run out of room. And at times you can't because of some obstacle (a barrier they put up or trees etc). And we've seen places that have said say no trailers over so big because of the road getting into the campground.
What has helped me is to look on google and see what others talk about and also look at the campground in the map section.
Also works the other way for bigger rv's. Before we down sized many times a campground would say max trailer listing at 40 foot or "pull thru's" but when you actually get there they might have a few that fit that description, but most are small.
It pays to do your homework the best you can before getting to campground.
But as far as measuring goes I do have a "fisherman's" tape measure that helps in my fish stories.