i have not done it yet, but i have cut one out of my doner truck. maybe seeing whats inside may help.
mine is from falling off a jack
i'm gonna cut out the marked piece, drill out the spot welds, and the rest with a cut off wheel.
here's the piece i cut from the doner after i drilled out all the spot welds, outside and inside rocker
weld up the holes and the butt weld the seam.
ABSOLUTELY - brace that shit first!!