The tool I used is the Blair Enforcer SpotWeld Drill. I also used the curved seem breaker tool.

The problem with the Seem breaker is it tends to rip the steel if the spot weld does not "pop" off right away.

With the Blair tool I was able to drill out spot welds in thick or thin metal.

Hear are some pics. Notice the clean drilled spot welds vrs the torn spot welds (using Seem breaker). The Seem breaker does not tear everytime but it would be very difficult to use on the rocker panels.