Put in chalk bags or bouldering buckets. Mesh covered to reduce dust & wastage. The stretched mesh lets out plenty of chalk each time to coat the fingers well but without losing too much powder and should last a long time.
While the indoors version is made with raw carbon steel with matte powder coating, this Outdoors version is made with galvanized steel with bright outdoors powder coating. Hence, if the pull up bar will be installed unsheltered outdoors, you should strongly consider this version.