Keep my garage moisture free

Another option is to space the boards away from your siding which would add an air space and the rigid boards themselves would not come in contact with the siding and condensation. Your roof has the purlins which will give you a 1¨ air space . Unfortunely due to the horizonally mounted siding you have no purlins on the vertical walls . After you cut your fitted boards you can glue several approx 4-6¨ strips of excess board material to the back of your fitted boards to give you a 1¨ air gap.