I'm sure there are lower tower strength's out there, but since I've only been focusing on the CHS District, I believe this is the lowest in our district:
Central Maryland - Chesapeake District Event. Qualification Match 45
Final Tower Strength: -6
AM: 1 Boulder
TO: 13 Boulders
Source:
http://frc-events.firstinspires.org/...lifications/45