EternalTerminal works great as a mosh alternative and fully supports tmux -CC
Alternatively, there's apparently a forked version of mosh out there with iterm2 support hacked in, but I've not tried it.
The real purpose of mosh is to make remote sessions usable over extremely poor connections (i.e. high latency and loss). EternalTerminal doesn't make your session work nicely from an airplane like mosh does.
The featuresets of Tmux and mosh conflict directly.