My grow-out tractor has a mostly roofed run. I put a large saucer from a planter in it, filled with plain sand. Any type of container that you can fit in there works. My chicks dust bathed in it and it didn't get wet, because of the roof. We moved the tractor daily after they got larger, too. We just popped the saucer on top of the run, since the run has a flat roof. The roof is hinged so it opens up, which also made it easier.
Once the pullets were large enough to not be so tempting a target for cats and small hawks, we let them free range all day. Even before that, we let them out when we were around to supervise or at the end of the day. If you can give them a little time at the end of the day, they can dust bathe in a dust bath out in the yard.