As shared above I have never found...."the animals can not be left unattended" to be directed to dogs resting quietly inside the coach. And if it does/did, I have never observed it being enforced even when I have stayed in Michigan state parks traveling to/staying for dog shows. Most reasonable individuals are tolerant if a dog occasionally barks from the inside as someone walks by a rig.
But I also know that the world is a big place and someday I too may be asked to leave a park because of having three dogs or because I left them in the rig to use the showers ???? who knows ???? I am not going to worry about it because the probability is so small. If I know that certain parks/staff follow certain rules, there are just so many other choices to make to worry about the ones that don't want you.
In NC at a state park one January....I even took Herschel into the bathhouse about 9pm at night while I took a shower.... The campground was "almost" deserted.... I sure felt safer having him right outside the shower. The state park vehicle drove by as I exited the bathhouse.....no one said a word to me....