Good looking horse.
What is his skin problem? Are you using a medicated shampoo for that specific issue? The bath and the brushing might not feel good depending on what the problem is.
It sounds like he wants to be responsive to you (since he seemed relieved to see you after an absence) but he is not thinking of you as the boss yet. There have been good responses here. And getting the trainer to work with both of you is a good plan! If you want to move him on the trainer may even know of someone who would like to have him.
I know it can be frustrating but working with any horse, rescue or not, has its rewards and challenges.
If you ever find yourself in a fair fight, it's because your tactics suck. ~ Marine 1SGT J. Reifinger