Don't bathe just yet. Use a damp washcloth to clean him and rub him down. Be playful and loving and do it in short sessions. One caveat - don't stop unless he is calm. If you stop when he is nervous then that is what he remembers - being nervous. But if you keep going until he at least calms down then end on that positive note and try again tomorrow.
Then wrap the brush in the damp cloth and begin to desensitize him to the stroking action of a brush. Eventually (but quickly enough) stop using the cloth and just gently brush him. Use a softer, boars hair type brush to start.
I am not clear on the 'whistle for barking'. Why not just use your voice?
Love Them & Lead Them,
~Elizabeth & Doug
Dog Training the Way Nature Intended