I don't think this will work unless you have a range of user and group IDs allocated for your user. Those will be used for non-root in-container users.
I know uid 0 in container will always map to uid outside the container (e.g. 1005), but I haven't tried e.g. uid 999 in the container to ensure it maps to uid outside of the container (again, 1005), does that work?