Only Bridge Bay campground is hard sided only, the 340 spots I was referring to, that is also the only powered campground in Yellowstone. It's actually silly because a Grizzly can hook the side of a locked hard sided camper door and pull it open almost as easily as messing around fighting a moving tent.
Grizzly Bear killed in the North Fork of the Flathead Drainage after breaking into camper | Montana Hunting and Fishing