Don't know what its called now, but they have those waterproof wall panels that plastic rivet on. We had that installed in our Ostrich incubating and hatching rooms, we could wash it with a 3000psi sprayer.
That's what I'm planning for the inside of the chicken coop, when we build it. For the raised planter, I want it to be part of the wood so nothing can get between it and the wood. That's why I'm thinking something painted on, so it gets into every poor and crack in the wood.