I have never seen such a thing. The steel one on my 68 has been on the car for over 20 years and a lot of miles and has no rust showing.
Too many short runs will build up condensation in the exhaust system and rust it out in short order, not
enough heat build up to burn off the water.
<p><font face="Comic Sans MS">100% Perfect Reproduction of Transverse Muffler used on 1969 Mustangs & Shelbys with 428 CJ/SCJ and all 1969 Boss 429s and Boss 302s. Price is for One Muffler (enough for one car). <font color="#0000ff" size="2">Click on picture or above link for more...