TTI Exhaust Longevity
The biggest enemy of exhaust systems is not using the car and letting them sit, even if you don't drive them in the rain. Just the humidity in the air while the car sits will start the process. My headers are not coated on my drag car and after two years have very heavy surface rust which will rust out eventually because it is not used enough to keep the rust burned off. The humidity can easily reach the inside also. Most exhaust systems rust from the inside out. Coating inside and out is the best bet.
Chuck