Wow, what a story.
1st welcome to YT. This is such a great site, everyone here is really nice and always willing to lend an ear or paw.
I do not have a 100% for sure answer, but sounds like his skin is so sensitive after everything. I know that washing removes the natural oils from the skin and coat.....is it possible that his fur is staying just a little damp for to long and that is causing some of the more recent problems. Vaseline would be a good barrier, messy, but a barrier.
Please keep us posted on his recovery.