Ah, thanks.
It seemed really solid and stuck on there, but it just ended up taking a bit of pressure in the right spot. I first pulled the top-rear edge out, the part that wraps around and faces the outside of the car. Then I used that leverage to slowly go downwards and remove the entire rear side, and the whole cover came off easily after that.
As for finding a ground spot, I needed to actually splice the door sill wires into the door switch so that the sills would only come on when the doors were open.