I have a set of TJM brush bars/side steps on my Defender.

In a couple of places they have rusted through so I'll need to remove them, weld up the sizeable holes (10 cent to 20c size) and repaint.

Is there some sort of treatment I can put inside them to help reduce chance of future rust?
Ideally something that won't get set on fire when I weld it.

Suggestions welcome.