I think that for port forwarding, it is always any internal port, and you specify the external port. In your case, just put in the ports 1200, 27015, and 27020 for external, and try putting "All", or "Any" in internal, or something like that, for UDP. Then go to "Port Range Forwarding" at the top there, and put in the port ranges 27000-27015 and 27020-27039, for TCP, into the external. Try variations of "All" and "Any", if you need to, try putting in a range like 0-99999 or something.
Also, if this doesn't work, just try switching external/internal.