Given how rusted the wire on the latch is, I don't feel comfortable trying to reshape it as I'm worried I'd break it. My stop gap solution is some balled up bluetack which fills the gap and makes the door unable to move.

Needless to say I don't want to leave this 'solution' in place. And am considering what to do to make for a more final solution.
I did have a registered electrician check the box a few months back due to the rust. And their professional opinion was that the rust was a visual thing and that the box itself wasn't about to break apart or pose a direct safety risk. And since replacing the entire box with a new one sounded like it would be quite expensive (electrician said I'd need to have power off for a day, including getting in the power company in to turn power off/on at the pole). I'm focusing on just fixing the latch for now.
My best thought is that I could get a different closing mechanism, then drill a few small holes and then bolt or rivet the new mechanism onto the door. But searching through what is available at places like bunnings I've not seen anything that looks to me like it would be ideal for such a job. Does anybody have any recommendations of something I could use? (or a better way of keeping the door closed)