Tell me when the reverse proxy is setup correctly for /mona/ or whatever you decide as a solution.
You should now be able to access /mona/ through I2P. I wanted to keep the boards on separate domains but it doesn't really matter. Choose your favorite domain and go to any of the 3 boards.
https://bbs.jp.net/prog
https://textboard.org/mona
http://textboard.i2p/sol