Reverse SSH Tunnel Issue

Question

I'm working on setting up an unattended Ubuntu PC with Ubuntu Server 12.04 Minimal, and since this PC will be placed in a remote location with no keyboard or screen (unattended), I need to have a permanent SSH connection from this machine to a middle-server (between itself and me) - reason being, this PC will be behind a NAT firewall.

I followed dot-to-dot instructions at http://wiki.fabelier.org/index.php?title=Permanent_Reverse_SSH_Tunneling but when I connect, I just get an error Quote: ssh: connect to host 5.175.145.251 port 19999: Connection refused So I went back googling for a solution and found http://www.alexonlinux.com/reverse-ssh-tunnel-or-connecting-to-computer-behind-nat-router

Surprisingly, Alexonlinux's solution worked out-of-the-box.

Seeing this, I tried the previous method, this time using Port 6333, but no luck. Then I tried Alexonlinux's method using Port 19999 and again it works fine.

The reason I can't stick to Alexonlinux's solution is, that it requires some commands to be entered on the PC behind the NAT, and that's not possible in my case.

I really wonder what could be stopping the connection when using Fabelier's method. Maybe the script is not loading? I did try manually running the script but still no luck.

I have also set

GatewayPorts yes

on the PC behind the NAT.

For the record, here's the script I've used from Fabalier's method:

a=`ps -ef | grep 19999 | grep -v grep`
if [ ! "$a" ]; then
    ssh -fN -R 19999:localhost:22 <middle-usename>@<middle-hostname>
fi

(obviously I've changed the @ to the necessary) I had to change the first line as brackets were not acceptable.

Would really appreciate some help on this, pls.