You should only need to forward a single port #, and here's how to find which one:
1.open ST
2.click Tools -> Statistics
3.scroll down until you find this line: "Outer IPv4 UDP Ports xxxxx"
4. this is the only port necessary to forward, and you only need to forward UDP packets (forwarding TCP seems to be optional, as i've got my router set to forward UDP only and it works perfectly.)
now, if you do this and it still doesn't work, you may need to do a fresh install. (note that there's a little more to it than just un-installing/re-installing. after uninstalling, you have to find the "hidden" ST properties folder and manually delete it before re-installing. if you don't do this step, when you re-install it will be set up for the same UDP port again.)
ST uses 15700, 15800, & 15900 on yourlocalIP, (i.e., "localhost,") but not on your outer IP.