After moving the sport mirrors forward on the doors and putting on small bumpers I now have holes that need to be filled in the sheetmetal. Some of these are nickel sized. I do not want to fill them with plastic could solder or lead be used?
weld them...if you can't weld...maybe try the "welder in a tube" stuff..i've used it on previous cars for random things...stuff goes abosolutely rock hard.
I used some of that steel putty once to repair the elbow joint in a 3 sided trimming unit that ran 12,000 cycles an hour at around 2k/psi for like 8 months while waiting for the replacement parts to arrive from Japan. Also used it to repair quite a few destroyed weld nuts. You just apply a blob, let it cure properly and then you can tap and die to your hearts content. I would not hesitate to use that stuff in ANY application. I've been considering using it to patch up some rust holes until I get around to doing body work on my car for real. Once you get it applied and properly cured you just grind it down smooth and spray paint.
I'd be worried about paint adhesion with some of that stuff. If nothing else, they make modern adhesives to bond sheet metal. Cut out an oversized piece of metal that would fit behind the hole and glue it in. After it cures, scuff it up and skim with filler. Filler is fine as long as water can't get to it from behind.