Travelling with Cats that like the outdoors

My parents travel with two dogs and a cat. When traveling they are in a crate. When stopped the dogs are inside are in a outside pen. The cat is inside or on a leash and they go for walks with the dogs and cat. Strange to see a cat on a leash but it works for them. Cat going in a out of the RV when home and dad is working on it or loading. So cat is ok the RV and its a safe place.