No pvc pipe style feeder is ever going to be rat proof, you need a door that closes tight, a material that rats cannot chew through, and a big enough difference between the weight and reach between the chicken and the rat to make it physically impossible for the rat to get to the feed. Reach in how far the hen can stretch out to eat, not in how far the feed tray is off the ground as rats can jump many, many times their body length.
That said, IF you start off with a properly designed treadle feeder with your adult hens you are far less likely to have a rodent problem during the few weeks your annual batch of meat bird chicks are growing to size.