I have a springer with what sounds the same as your dog. Merlin is an indoor dog. I started giving him a cayene pepper capsule and a oil Pill(its a combo Flax,fish,and borage from Rexall) each morning and it is clearing his skin and helping with thin coat.
Do the blisters smell? Merlins do and the vet has no clue what we are dealing with so I started studing nutrinets and came up with this. Its been a month and His body whitch was covered, is almost all cleared up.I am also bathing him every couple weeks with a puppy shampoo,Like a baby shampoo. I had to shave him bald to start this so your dobie is already to start . I just scrub the heck out of him to try to get the blisters to erupt and get that yuck out of them.
Hope it helps if you try it.