Just had a big success straightening my front bumper on the Cossie. What I did was heat the front bumper with an infra red paint curing lamp (must be short wave not medium wave as short wave sends heat through the paint and heats from the bumper itself) at about 12 inches away for 10 minutes and then removed the lamp and drove a fork lift truck into the mouth of the bumper with lots of rag around the forks. I gently raised them so the bumper went higher than level and left it there for about an hour to cool properly so when I removed the fork lift it settled down to level. On the next one I do I will remove the thin panel just below the grille so it doesn't bend too.
Just thought I would pass that on as it pisses me off to see it sagging.