@jaredbusch Awesome. I'm going to try this.
I was just about to followup with this, saying that I was able to get it working, by not using any custom rules at all. Since the IP that I want to allow, is my local office, which is where I want to connect to the mySQL data from, it works already. Reason: I have my local office IP listed in the Trusted Network area of the Responsive firewall.
Of course, to get this to work, you have to change the listen address (bind address) in the etc/my.cnf file to listen on your public address, other than the loopback address.
I would probably change it to listen on any to have one thing less to remember just in case something changes, but that is just personal preference.
Oh yeah, I did that actually. Then I created a user with select access to the crdb database. The root user by default, on FreePBX installations, has no password. However, the root user can only log in from the local server, so I don't see a need to implement a password. Unless I'm missing something....