When it comes to patching a rot hole on a complicated angle, you would think welding in a nice square piece would be ideal, but actually, some skilled bodymen prefer a patch with a more rounded shape. The sharp edges of a square can hold heat, unlike an obtuse shape, which distributes heat more evenly. If a panel gets too hot in a certain spot, it can warp the area, causing you more work. Rookie welders should practice welding with different settings on some scrap metal before attempting to “fix” anything permanently. Some, if not most serious rot repair jobs should be handled by a professional if you want to remedy them for good, but if you’re daring, broke, and/or comfortable with your mistakes, try it; they say practice makes perfect.