How to set up port forwarding to access TrueNAS Scale homeserver from outside?

I'm quite happy with my newly built homeserver using TrueNAS and some spare hardware. It's been working nicely. But now I got really stuck for the first time. I want outside access, which means getting the correct ports forwarded, getting a name or DDNS, and possibly an SSL. So I forwarded ports and nothing's worked. My network topology is like this: An Askey RTF8115VW modem from ISP with external IP matching the public IP. Said modem internal IP 192.168.15.1 and distributes IPs in the 192.168.15.1/24 range. A mesh set with external IP 192.168.15.68 and 192.168.68.1 as it's main IP, distributi

Question by Fernando D'Andrea on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.