"Also, does the rash ever plateau or does it does it continue to get worse and then subside after treatment?"
My husband's moved around - started on top of his (bald) head and face, meandered down his chest, popped up on his back, returned to his head. His rash took about 5 weeks after the final infusion to clear. He used aquaphor, and minocycline oral antibiotics. The aphaphor made a big difference. He also used some cortisone cream on his face when it got too itchy.
The intersection of the radiation burn and the rash was the most difficult to manage - for the last couple of weeks of radiation, he switched to the high-powered burn creme.
The other thing you may hit toward the end of the
Erbitux infusions is cracking in the skin of your fingers and toes. This pops up at about week 8 if it's going occur. I had to badger my husband to use the aquaphor on his hands, too, but it did help.
Good luck with your therapy - and stay as hydrated (inside and out) as possible!