shaving cab seam

[dirrty d84]

i am trying to shave the top cab seam on my truck. a friend of mine used body plastic and on the thinner spots it cracks through. what would be the best way to do it if anyone has had expierence with this i would appreciate your help.thanks

[shaved80]

you can either take your time and weld it, but go realllllly slow so you don't warp it. or use kitty hair, filler with fiberglass strands, to first fill the seam, then regular filler to smooth it out