pylon:
That's not possible, you have to forward to a specified port. Else, how would the Yun shield find out what to do with a packet received on port 12345? Forwarding always needs a target IP and a target port. The port number may be the same but it must be predefined.That sounds like a network problem. How did you configure the Yun shield? Did you set the WiFi interface to be the internet connection?
I did not know it needed to be forwarded to a specific port, not just the address. As for the luci interface, I can access it fine, both from the WiFi on my local network of via the ethernet connection. I was meaning trying to connect to 192.168.1.111:12345 (which I thought would've been forwarded to the PI) resulted in the "page cannot be reached". I just reconfigured the PI to have its http listen on port 12345 and forwarded anything on 192.168.1.111:12345 to 192.168.241.3:12345 and I can now access the web interface and camera stream of the PI through the Yun shield just the way I was on the local network! Thanks! (This is an important step in a 3g-networked-go-anywhere-remotely-with-a-cell-connection-bot 
)