If it's only on his heels, you could leave his feathers on, unless the skin is getting wet through the hair, if it is, then take the feathers off so the skin can dry naturally. If he has a lot of hair where he's sore, then trim it off with scissors.

You could try mixing a jar of vaseline with a bottle of wound powder ( need to heat the vaseline a bit first so it mixes well).

 Don't wash his legs unless they are wet & muddy If they are, then either wash & dry thoroughly or wait till they are dry & brush the mud off before smothering the mud fever with the paste to protect it - the next day, just wipe it off with some paper towel & re apply it.

You don't want to keep washing it, you want to keep the water out.

This was a remedy from a vet & i know people who have had very good results with it.

in your situation, i would def give it a try as you won't be able to dry him well enough.

i would be wary of using pig oil as some horses can react badly to it.

Good Luck

Pig oil and sulphur are very good to prevent mud sticking to his feathers. I wouldn't clip his feathers off as they helpto keep the mud awat from the skin. My old gypsy cob had loads of feather and she never suffered with mud fever but my cobxtb who has no feather has suffered with it in the past.

Feathers may actually hold the mud and water to the skin if they get very wet, having said that though it is a real shame to cut them off.  You could try "waterproofing" his legs and his feathers by coating them liberally with cooking oil before turning him out, then when you want to rinse the mud off his legs it will slide right off.