I think the OP has the right idea - be able to prove with a REAL certificate, that the dog is well-trained and well-socialized. My experience has been that RV parks will fudge the rules for "good dog owners"
I was surprised, as we pulled into our RV site, to see 2 Dobies in the site next door, in a "restricted-breed" campground. And then I saw why - they were loose! There was a thin string laying on the ground defining their space. Those dogs were trained beyond perfection. I wandered over to their owner, to apologize for the rude behavior that was going to erupt from my rescued Cattle Dog, (who had a real hatred of large black dogs). He laughed and said "not a problem" - every time we passed, he somehow was able to make his dogs "freeze" - Jack never knew they were next door.
