I self host a small Discourse instance, and it is very easy to setup and manage, for someone who knows how to do similar things. It all runs in Docker containers, and setup is much more complicated than just editing a docker-compose.yml file, but the necessary documentation exists, and is easy enough to follow the instructions.
It works fine behind a reverse proxy, and seems to play well with others. Mine has it’s own hostname, and is hosted on a server that hosts web stuff, too.
The data is trivially portable. I’ve not yet had to restore my site, but it does make automated backups, which can be restored.
The technical aspects of recreating the board are very easy. It is only the legal aspects.
It would also be pretty easy to restore the board, and then strip the SDMB branding. So getting permission to use the content could be separated from using the trademarks.