#1.
Grind back the area which you be welding the filler plate in.
You want them to be as even as the door skin as possible, so use magnets to hold the filler plate up to the edge. This also saves you a hand from holding them.
#2.
Begin tacking the panel, using as little heat as possible, and making the next tack as far away from the last as possible, ie tack it on the left, then on the right, then maybe the top, then bottom, ect.. I use an air nozzle to cool the weld after its made to keep the heat down.
#3.
Finish tacking all the way around, keeping the heat very low, until you have a constant bead or very little spaces between tacks. Then grind it down, but take it easy with very little pressure or the heat from the grinder will warp the hell out of the panel.
#4.
Once the grinding is done, slap some bondo on there and let it dry. I kinda went overboard with it here haha but I hate bondo. Its ok because I have a body file or 'cheesegrater' that will knock that down in seconds.
#5.
Im not going to go thru all the sanding and work getting the area straight, because thats commonplace. You want to keep checking the area when youre sanding with a straight edge to find any high or low spots, and sand or fill as needed.
