Don't understand why you guys are doing this.....though I did miss the horror stories someone referred to above.

Most pipes I'm familiar w/ are double wall from 1/3 to half-way half way down; WREN's just use a much shorter section (maybe 3" long....the 'cookie cutter') that slides over the (inner) pipe end; this way the inner pipe can be cut to optimum length. The CC rear edge should extend a half-inch or so beyond the end of the inner pipe edge to promote venturi-type cooling. Front/bell, centered, and affixed w/ the four straps approx 1" behind the engine rear exhaust nozzle edge. Inner pipe is robust, installation is quite secure. But that gap of one-inch is most important...infact WREN says 30mm (about 1-3/16")...otherwise, the pipe might collapse being, starved of secondary air. Inner pipe then rides in the CC during expansion/contraction....CC can be affixed/held positioned by a rear wood former, etc. I've used two short 2-56 SS screws to either affix CC to the inner pipe so any sliding needed is the CC in the former. Or, SS-screw the CC to the former; inner pipe slides in the CC. That part....the drilling/screwing is, indeed, a bit tricky.

Pipe runs cool....both Golds and SS. Unless you have some very minimal clearance in the rear fuse, say, less than half-inch distance from combustibles.....why are you fashioning a full length outer wall? What are those 'scare stories'? Tx!

Ray