I've had great success using Nizoral (1% ketoconazole) shampoo to control the acne and oily skin I get on my back with TRT.
I rub the lather all over my back and any other problem areas once per day in the shower, leave it on for 5 minutes, then rinse it off. I notice a huge improvement when I use it consistently once per day. I also use it on my scalp to hold off any baldness, but thankfully that hasn't been a problem for me yet.