Hello,
IF you do take him to the vet please do not let the vet give him a medication called Ivomec or Ivermectin. It is contraindicated for reptiles & really should not be used. It causes way too many problems & can become very toxic to them.
Continue with the treatments & when you have him in the
bath, try to get them off of him while he is in the
bath.
Did you wash & bake all wood items in the tank? The mites will infest the wood & will continue to get on him.
It is relatively easy to get rid of mites, but you have to take everything out of the tank & replace it or clean it really well.
The wood can be soaked in hot water & baked for 30-45 minutes at around 250-300 degrees.
Good luck.
Tracie