It's always an issue with putty, the easiest way is to get some pipe the same size as the one you got on there, and cut the shape you need to fit, then weld it up, just spot weld and test fit then weld off the car, we did from centre to back and just welded the whole thing and rtv on the c clamps. As for the back box we just had a universal strap which sit in one of the rubbers nicely. My car is fairly loud when you floor it, but at cruz it's just a little bassy. Not to bad to be fair. A very unique but racey sound. And that's a lot of work, hopefully it all pays off soon