My duster had flex pipe on it from the head pipes out with mufflers in between and it leaked so bad there was barely any sound behind the carYa use flex pipe if you want your exhaust to fall off !!!
Move a way from the flex pipe sir.
Unless your talking the expensive stainless weaved flex? I have used these with excellent results. Just for that little bit of give in the system. Especially at the down tube, right before the "H" pipe. You only need one.
Something like this.
Exhaust Flex Pipe Stainless Steel Double Braid 3" x 6" w/ Ends 10" OAL 30006DN | eBay