If you spend any time at all at the Linux command line, you need tmux. Period. It makes you orders of magnitude more effective, there’s just no excuse for not using it.
Given that the RN312 NAS is x86 based and using Debian Wheezy, there’s an already compiled package for it. Installing it is trivial. Just ssh into the NAS, then issue:
apt-get intall tmux
That’s it. Copy in your favorite ~/.tmux.conf file, and you are set.