hex0rz
+1y
Actually, it is a PITA to try and cut out a piece without something to really go off of. Burdaddy, what I would do, is cut out a piece of metal about 1/2" larger than the whole your trying to shave. With that said. Take like a magnet or something you can hold the piece of metal with and hold it to the door on the inside.
You will need to cut out the area on the door first as well and shape the metal to the doors contour. With this said putting the shaped piece of metal on, you can then successfully trace it out and then cut off excess!
When you go to put it on, it should weld in flawlessly and there will be very little gap between the door metal and the filler piece! Given that you know how to compensate for the grinder, etc. when cutting out the trace!