Our dirt is loose enough for the flock to dust bathe just about anywhere, but even though I'd do outings with them, when they were a month old I filled a container with wood ash and would come into their room and find totally gray chickens.
I almost wrote kittens for some reason.
Anyway, I think my chickens would love a small used tire as a perch and dust bath combo station. I've been thinking a lot about this lately. It would be a great place for them to gather around for conversation while two or three are zombifying themselves with wood ash and dirt.
Chickens get bored, so it's my guess that if you give them something exciting like a tire filled with bathing material, it'll be a big hit, and I think they'll enjoy the warmth when the sun warms up the black rubber.