long strand fiber glass, push it in and smear it around on the backside, make sure it has a good bite. it will more than likey sag a little bit but you can sand it flush and then use some regular body putty or glaze for a nice finish. done this with two trucks now, works like a charm and no cracks.

 

brass behind the hole then weld. but idk how bad it'd warp

 

take a piece of 1" or 3/4" copper pipe and cut it to a length you can work with. flatten it out with a 3lb hammer. if you have a 110 mig welder put it on its lowest setting or what a chart recomends for the type of wire it has and the thickness of the metal. put the piece of copper on the back side of the whole and make a like a tac weld and fill in the little whole. the weld wont stick to the copper. so the back side will be nice and flush then take your grinder or polishing grinder and grind the outside part of it down nice and smooth. it shouldnt warp. if it does your putting out to much heat or are welding for too long a time. if you use a polishing wheel you shouldnt have to use to much filler on it. if you do use the new bondo/glass stuff they have now. much stronger and is waterproof. good luck.

 

^^ that too. it wont stick to brass either. which works out if you have a brass hammer layin around like i do

 

I used my hogan mag drill to make plugs drilling out 1/4 plate. I then used the mig welder on low heat to tack the edges in. I ground the weld flush with a flapper disk on a 4 inch grinder then covered it with a thin layer of bondo.