Yeah it's a hard topic to search for.
Try this one.
http://www.myswag.org/index.php?topic=19177.msg297385#msg297385Came up under a search for "caravan parks".
Yes, some parks enforce the rule.
When booking ahead, if staying in a CP we always ask if there are sites suitable for a CT available.
Sometimes, we turn up and look at a site, and then ask for an alternative one, but if it's peak,season it may be hard to get an alternative.
Generally, you can get around it somehow with a bit of communication beforehand.