I have always heard not to bathe a water dog very much at all.It gets rid of the natural oils in their skin.I guess the newer shampoos are better,but unless the dog just rolled in the stinky,don't bathe it
And salt water is supposed to be good for them.That's were I bathe my dogs.
Yes without soap. Sheez,if I give them a proper bath,they are for sure to find a week old gutpile to roll in.
And I am with spending the $300+ on trying different foods.Lots of great foods out there that are made for dogs with allergies. $300-400 for a vet may not get an answers any how.
Good luck