You are right, normally you just have to configure port forwarding of port 9901 for you pi's ip in your router and that's it. A full configuration manual has been primarily in the initial post of this thread, but unfortunately, after the "get 10 ppc for a full node" project has ended, this manual has been removed. Don't know why.
Maybe there is a chance to restore this manual somehow. Or we update the initial post of the peerbox support thread and add it there. Will put it on my to do list.