Sandblasting can warp panels. I prefer Media blasting. But this stuff can soak into places sand or any media can reach. I want to retain the factory spotwelds so I had to leave a piece of the 1/4 on the gutter. Mine had some holes there too. Soaked in that seam so I won't have to worry about rust coming back. When done I will use panel-bond to clean up all the seams and assure no more leaks.