When I was in the Navy and stationed in Guam, I had a co-worker who would ride his bike to work every day and park his bike in the breakroom. He also had a problem with flats. He tried everything; replaced the rim tape, replaced the tube, replaced the tire and eventually replaced the entire wheel with no success. As it turns out, another co-worker was letting the air out of his tire everyday. Sometimes the simplest answer is often the correct one (Occam's Razor).