The bracket in the door frame that holds the driver's door check is
loose
on my car. I presume that that is what you're welding.
No, the door itself was rusting apart in my case, the attachment
in the frame was fine.
So how does one do the welding?
Umm, carefully? Grab welder and weld anything that looks like it
needs it. Have hose handy for putting out fires. Lots of wet
towels to drape around to catch sparks.
It helps, of course, if the car is a heap and you don't care what
it ends up looking like. When cosmetics count things get a lot
harder!
-- Jim