That's what I've told everyone and all they say is it looks good or fine. Well that's cuz it's not there's. and I know I'm putting black Bedliner on the bottom half for new paint but it still warped
He'll have to shrink the metal first, which can get tricky but you can do it if you heat it ups be quench it with a rag dipped in ice water, and slowly hammer it lik you say. Problem is that'll weaken the metal
It was welding, he started on one side and it got hot and it warped in and he had to pull it out and it was not good.
If you want my honest opinion, you can spends hours trying to fix that, take and hour an a half to cut it all out, reweld a new piece, metal finish, skim coat, block, and spray some 2k primer on it