I’d hoped to simply patch the rusty bits on the Mini’s door, but welding a large, mostly-flat panel without distortion is difficult. It’s far easier to just fit new door skins.
I used an angle grinder to grind through the folded-over edge all the way around the door panel.
Unsurprisingly, the door frame needed some rust repair.
The new door skins were tidied up around the edges…
The edges are carefully folded over…
It’s important to test fit the door, because the fit of the outer skin can change the door’s shape. Once the door was twisted into the right shape, a couple of welds on the door skin locked it into place.