I have been toying with building a muffler that would be in the neighbourhood of 2 x10 x15 inches and placing directly under my turbocharger since its elbow faces straight down. so the input would go in from the top of the flat side and output would come out of the top and then out the side with nothing showing but a straight pipe down the side. I figured since my sump is 2 inches below the frame rail I might make use of that space. I have some 16g stainless sheet that I could make one out of it I thought it could flow reasonably well and quiet it down a tad.
Dale

It would seem to me that a box too close to the turbo could impede flow or at least disrupt it. You could, of course, build the primary pipe into the box so that the first run of pipe inside the box would go the full length of the box and then turn on itself and woosh back up the box before turning tail and scurrying back towards the blunt end. If you see what I mean?