Since I dont use this car in the winter, I'm OK with drilling little holes underneath for mounting brackets, in this case for the skirts.
Imagine my surprise when I punctured the right side rocker panel:
It ran for a surprisingly long time! Maybe a cup or 2 of water came out.
I'm not sure how the rocker is supposed to let rainwater out (or how it gets in), but this one is obviously blocked... or used to be.