Originally 18GA., or at least that is what I mic'ed it to be. Of course there is a reasonable margin of error on my part when you consider the curve and paint on the part I measured. Anything thicker is a real bear to work without the proper tools/skills.

New parts are probably 20 GA. A new stamped part, even using a slightly thinner metal, will be plenty strong when you consider the forming of the shape adds strength.

The very first thing you need to do is determine the extent of the rust. The second is to discover what caused the rust. Third is to remediate the cause.

Are you able to post pictures? They will greatly help in deciding what course of actions you should/can take.

__________________
“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now