Well, to start with, I wouldn't be buying Mac. If you don't want to worry about rust, buy some quality stainless products.
I have a tid bit for you about MAC exhausts.
I put a full system on my Capri shortly after I bought it, drove it in PA winters for 3 years, parked it in my yard and decided to rebuild the engine. Didn't have a garage and planned on doing it quickly, but lost my job shortly after I pulled the engine.... so it sat in my yard, in the grass (that eventually turned to dirt) uncovered for the next 5 years. Got a good job and decided to do a resto on it since it had pretty much gone to crap from sitting so long. I ended up replacing just about everything mechanical on the car... except for, and get this.... the MAC exhaust... because it only had surface rust, but was otherwise perfectly intact. I finished that restoration 15 years ago and I'm STILL running the same exhaust with no rust through.
Put a MAC exhaust on my car.
Ran it for 3 years.
Removed engine and let car sit outside for 5 years.
Restored the whole car except for the exhaust because it was fine.
Have been running the car with that exhaust for the past 15 years.
So my MAC system has lasted a total of 23 years and still going strong.
MAC gets my seal of approval.