After being given lots of lotions & potions & advice from my vet on various occasions I have found Equine America Fungatrol to be the best thing for my horse. I shampoo and leave it for a while then work it in circular motions to try & remove some of the scabs.
I then use either the spray or the cream once she is FULLY dry. The cream is quite greasy & helps when removing the scabs and the spray is good for when the scabs are off & the bare skin is left.
Unfortunately it takes mine weeks to heal, on average about 3 weeks. However this depends on how big an area is effected and how well you can get the scabs off I guess.
After having 2 episodes in mid summer, one when I was on holiday & entrusted her to someone else and one when I didn't realise what rainscald was I always either rug her or bring her in when it's raining. It's a real nuisance but a necessity