So you decided to put something in your Cobalt's trunk and it won't fit like 12" bass speakers in a box.
Cobalt Trunk Panel:
The black bar in the trunk can be removed with a hard pull upwards (if I remember)
I tried to get it out years ago but had no success and didn't want to break anything. Recently I got it out yanking on it.
Why would you want to remove it you ask?
In order to replace the battery this thing can be in your way.
It has a lip that is flat on the bottom right on top of the battery area.
You can see the lip here going over the battery.
The cover is in the way but you can just lift the battery and replace without removing the trim panel.