Where he is going to have trouble finding a Catholic Church is here in the south. There just isn't a very large Catholic population down here. The nearest Catholic Church to me is about a half hour drive. In relation to the trail and small towns? Good luck!!
You might want to contact a guy named Circuit Rider. He's a pastor that hikes the AT every year. He may be able to help. Below is his website. He makes it to service every sunday, although he doesn't have the Catholic restraint, he may know of some churches off the beaten path.
www.heartbeatat.com
good luck