Here another optión, a inox Steel "Tip" bolted instead of welded. The tip is from the OEM exhaust of a VAG TSI 2.0 engine (Of my car, replaced by a Magnaflow muffler).
I just cut one of the twin tips from the VAG muffler, and take it with a friend who does work with stainless Steel, and he weld two Little plates of inox Steel with the holes for the stock bolts, and Voila!
Here some pics:
so there is a gap between the hole on the box and the tip? I hope you don't get some radiating heat coming up into ur *** and legs that will suck!!