Looks like it rusted thru from the inside out! I had a 2003 that leaked water in to the trunk. Couldn't find the leak for the longest time , even took the rear facia off, and couldn't find anything. I finally found the culprit, it was the trunk seal that would allow water to travel up hill back into the trunk at the seam. Once I sealed the seam problem was over. In the mean time trunk got rusty in the wheel well.