Thought I'd throw this out for some suggestions and ideas.
Our Hav -Shih Tsu cross, Bucky, has some serious bath time anxiety. Baths are not fun. Took us a while to clue in but we believe his anxiety is related to an accident when he was only a few weeks old where he fell into a water barrel and nearly drowned. I have been giving him a good brushing prior to baths, and noticed he starts trembling when he hears the water. We've always tried to make bath time a positive experience for him, but he hides when he realizes the bath is for him. He'll do just about anything for treats, but not even a treat will coax him into a bath. He goes wild to get out of the tub. It takes two of us, one to hold him and one to bath him. We both are consistently calm and speak softly, and try to make the bath as quick and painless as possible. I feel very sad that he's so frightened he's trembling.