It seems unlikely, but is worth checking. I assume a mothballed ship cannot move in combat. But :

1) Can a mothballed base/ship fire its weapons against attacking ships/fighters ?

2) Do its shields/shield regenerators and armor work, or is it a sitting duck with only its components damage resistance ?

If mothballed can defend itself, then there is no limit to how much you can build for defenses since they do not count toward the score determining MEE and cost no maintenance !