Rainscald is extremely rare in rabbits, I think because it would be rare for them to be out in wet weather on a consistent basis to set the conditions for it to occur, like it does with horses. In fact it's so rare that through doing a search, I could only find one account of it occurring naturally in rabbits, and it was with a wild cottontail.
I would want to find out how that diagnosis was reached, as it's possible the skin condition that this rabbit has may have been misdiagnosed, especially if the vet wasn't an experienced rabbit vet. I would want to know if any testing was done to confirm this diagnosis, or if not, were other more common skin conditions ruled out first(eg. mange, fur mites, fungal infection, treponematosis, other bacterial infection, sebaceous adenitis) before concluding it was rainscald that was the cause. If it was misdiagnosed, it's likely the skin condition can be easily treated once diagnosed correctly, as most skin conditions in rabbits can be cleared up once they get the right med.
If it's certain that this rabbit does in fact have rainscald due to testing done to confirm it, there really isn't a whole lot of info out there about it due to it's rarity, but there was this page that I found.
http://wildpro.twycrosszoo.org/S/00dis/Bacterial/Dermatophilosis_Bears.htm