What is the humidity? You may need to get a dehumidifier (or you may have that option on your A/C).
I also have my chins a room in my modified garage. Humidity is generally around 20-30% in the summer and can get up to 50-70% in the winter due to all the fog and rain we get around here in CA. I sometimes use the humidifier option on my A/C when the humidity rises a bit too high. I have never had any problem with condensation... my building is not made of steel though and there is quite a bit of space between the drywall, blow-in insulation and the outside wall so there wouldn't be such an extreme temperature difference causing water in the air to turn to condensation.