Copper weld thru primer applied along all seams being welded.
I cheated and panel bonded this one area because I didn't wanna lay in the trunk and weld it.
I got the quarter welded to the door striker and it fought me! The quarter had a bulge to it and didn't follow the door so I had to pull it in with a giant c clamp and it took a lot of trial and error but it's now better then it ever was!
You can see where it was fighting me by the worn off e coat