There are 2 ways to repair a panel that has bowed from welding. The panel has bowed because heat from the weld has actually shrunk the metal in the heat affected zone. The first method is to try and stretch the metal again by hammering your welds. This could be difficult if you have used a MIG welder or a lot of filler wire, and where access is limited. Really you should have hammered it as you welded. If this is not too successful then try the heat shrinks. Try to read the panel to determine where there is an excess of material. Using an oxy-acetylene torch, apply heat until an area of about 1/4" is red. It should rise up into a small peak towards you. Hold a flat dolly behind the panel and hammer it with a wooden mallet WHILE IT IS STILL RED. Use several small shrinks instead of a few large ones as the panel will get away on you very easily. You can stretch the shrinks out again by hammering "on dolly" with a steel hammer. Good luck.
