TTI Exhaust Longevity

I have TTI 2 1/2" exhaust on my car hooked to the stock 340 manifolds. I got the Dynomax mufflers from them also. I have had it on the car for about three years now. Car is always garage but I got caught in the rain twice. No a trace of rust on the system yet. System still looks nice and fresh and fits really well. No leak issues anywhere either.