Inspired by the popular PVC bucket feeder. I built the feeder into a box that was then secured to the supporting studs of the run. It can hold a 45lb. bag of feed and, as the original design, is fairly resistant to chickens that like to pick the feed out first (I had a problem with one particular bird, Scrambled). It is filled with a door on the outside of the run and is secured with a carabiner, like the other doors of my coop. I used 2x4s as the basis of the measurements so it's not very thick but it was 44" between studs so it amounts to a moderate sized box. Total dimensions: 44" x 20" x 4"
I hadn't considered it but I live in Southern California. The run is covered so it doesn't get direct rainfall. Sprinklers & splash may be an issue, though minor.
