I am unsure of what the honest expectations really are in this. There are 'Sheetmetal Repair or Replacement Panels', -and there are "Patch Panels".
Correct me if I am wrong, but the term 'Patch' tends to imply it is a method to make something serviceable again for a short period of time until proper repair methods can be performed. Generally speaking, the word Patch and the word Repair are not really synonymous. Rusty is correct in that Howell's patch panels do not even remotely mimic a quality fitting original panel, ...however if we are being truthful with ourselves, we are paying for a 'patch' and not quality. Quality pieces come with a price.
Joe, although I have always used AK (-or DQ) sheetmetal because of it being more forgiving to deep-forming, I have not noticed any susceptibility to premature rusting with that metal. Most of the 'patch panel' manufacturing is performed stateside, and one such company even offers complete bodies.
Interesting comments on your experiences nonetheless.