Note that the version in FreeBSD ports was a bit out of date and they changed the command-line flags between then and now so I built the most recent version from source and had to make a small change in CMakeLists.txt in order to be able to build it, for which I submitted a separate PR.
If these two PRs are accepted and a new version of Eternal Terminal is released with these changes included then I can ask the FreeBSD package maintainers to update the port and for that rc.d service file to be included in the FreeBSD port and package.