Yes, I use port 443 instead of 8080 for my CP. So what happens when you go to https://myfixedipnumber:8080
from inside your LAN?
If that works the same as https://192.168.x.xx:8080
then all is well and you are only missing a domainname and DNS resolution for it.
Have you got a registered domainname you can point to your external IP?
If not then you could try to emulate it with either Bind and use, say, one.lan two.lan three.lan kind of hostnames with lan as your private top level domain (TLD) or use "ip hostname" mappiings in /etc/hosts on your server and workstation. But, this won't work from the outside world so of limited use.