Sheet metal template?

thanks for the replies! I did plan on just replicating the drivers side, and just messing with the sheet metal till it was close and as stated, body filler to make it perfect.

Yea it was rusted through. What i think happened was poor weather stripping in the trunk, and then some water just sat at the bottom corner, and seeing the car was parked on like, a hill like yard, it just rusted through the corner!