The po cut the fenders to much so I get mud and water in the back hatch when I wheel. How do I fix the seam and huge hole weld it? And I just painted the whole thing so I dont want to burn the new paint up. I tried the expanding foam from the inside but it didn't work

 

The pinch seam in the rear is structural. You need to patch and weld.

 

I spray foamed mine. I used some cardboard wedge up in the wheel well so the foam doesnt fall down onto the tire while its setting up

 

What this guy said... your unibody is weakened until that is repaired.

 

x3, get some thin plate and patch and weld it.