The doors are actually Rusty the bottom but on the inside of the seam. Sort of where the lip is, where the inner and outer skins join together. The guys doing my restoration said that to fabricate a new piece then weld it would cost about £200. It is purely because the position of the rust holes are so awkward to get to.
I will keep the old doors and maybe look at restoring them, do you know how to separate the inner and outer skins?