How about 1/8" SS and then weld on the cut-off tiangles as stiffeners from bolt holes to exhaust hole?

If I'm not mistaken, Tracy said he made some flanges out of 1/8" steel (don't recall if it was stainless), and I guess they worked.  Seems like he felt that was pretty minimal though.  I don't think I'd hesitate to use 3/16".  Personally, I'd probably rather use stiffer material, than go to the trouble of welding the stiffeners on.  

 

Cheers,

Rusty (I would of course cut them for Ed)

Yeah, but tigging is so much fun and stainless is so honest ... Jim S.