Sure I could buy and add another device, power adapter, cables, etc. and then power yet another device 24/7. That’s not sustainable.
I could also install a gasoline tank and a generator in the trunk of a Tesla to achieve the advertised range in winter.
But that’s not the point. The manual says:
Objective: Enables a web surfer to access your Sunrise Internet Box (with no fixed IP address but
only a DNS entry) through a dynamic DNS provider such as, for example, dyndns.org."
The Sunrise Internet box currently does not provide that service for “web surfers” inside the network.
Please either fix NAT loopback or mention the defect in the manual.