My friends mare had mud fever a few weeks back. She lives out 24/7 and parts of the field are very muddy.
She just washed the area and gently rubbed off any loose scabs each day, then dried the area and applied Sudocrem. It cleared up pretty quickly like that!!
Apply a protective barrier before the horse goes out. I use NAF Mud Guard, it's very good. You can also get it as a feed supplement to help prevent it coming back.
I have found the best cream, bar none, to be Aromaheel. This stuff worked absolute magic on the quite severe mud fever suffered by the horse I ride. It also smells yummy!! I'd really recommend it.
Iv'e been using NAF mud guard feed supplement and after 8 years of struggling and washing with hibiscrub and every imaginable cream and lotion, he is finally clear of sores, I just keep him clipped around the heels and give them a wash with hibiscrub if a sore starts to appear but this is only necessary every few weeks now. He has been on the supplement for about 2 months now so just thinking of taking him off it to see if it stays clear. He also has pink powder as he suffers from digestive problems too and think this has helped. His heels do tend to flare up the same time as his tummy troubles! good luck..