You can only connect through a ssh tunnel using the public key that you create in Forge (Server Details/SSH Keys). You also have to do that in order to ssh into the box, so you may already have one set up.
I don't use workbench, but here's what I have to do with Navicat and Sequel Pro:
General Settings:
Hostname/IP: localhost (sequel pro required Forge server IP, navicat required localhost)
Port: 3306
username: forge
password: forge-password
SSH Settings:
Use SSH Tunnel: (check)
Hostname/IP: forge ip
port: 22
username: forge
authentication method: public key
private key: /path/to/key/on/your/computer/keyName_rsa
passphrase: your keys passphrase
@CRONIX - Thanks alot.. I actually got to make it work.... funny enough that I wasnt patient enough to thoroughly go through the settings you sent me and I was missing the General Settings tab section. I keep using General setting for SSH settings and this has cost me a week and 3 days... Thanks anyway