Sentinel isn't involved. Stand in a base and type this in the chat window:
/demorecord yoursgname
/demostop
It takes effect instantly, you can demostop right after you start recording and you already have everything you need. Look in your coh install directory, there should be a folder called client_demos. Inside of that find yoursgname.cohdemo and copy that file somewhere safe. That's your base.
A solution for locked characters unfortunately isn't possible from our end.