I wouldn't be using an iodine shampoo on him. You're drying out the skin and there isn't anything you're trying to control with it.
Depending upon the severity of the burn/peeling, I'd give him the rest of the summer to get over it. If you think it's allergy related in any way, go ahead and test him now. That way you'll know how to manage him next spring/summer. Always have 2 long flymasks around for him and they only come off at dark.
Any alfalfa or clover in his diet? Those can make him more sensitive to sunlight and more susceptable to bad burns.