Gents I am a plumbing contractor by trade so please excuse me if this is a bonehead DIY question but I need to know. I have a Millermatic 130XP and I want to weld "Pypes" brand SS exhaust piping (409 SS they tell me) . The project truck is frame off so I can tack weld and then remove sections to get it in posistions other than up-side-down for welding. The pipe is not thick* so am I right in looking for .023 diameter wire and what would the "Call-Out" be for the type of wire? I do not think I want a super hard material. I am kinda lost here so any help would be greatly appreciated, including where to buy it, and of coarse I only need a small roll. My research says I should use TriMix gas as well yes? I know i could use my standard wire but I do not want rust to show up.

* I will need to weld up header flanges so my system is modular and that is thick to thin material but most of the work is thin.

Thank YOU!