In addition to the heat concern that Harry mentioned, if the pipe ever failed at the seam you will fry your fuse. A dual walled pipe offers another layer of protection. By the time you add the extra insulation to the rear fuse there is no weight savings for a single walled pipe.

Gary Mueller at Jet-Tech makes a dual walled version of the Wren pipe. I had him make a 54 size pipe for my Maverick, which I am converting to turbine. It is stainless steel with a titanium outer wall and appears to be well made. He can custom make it to any length.

http://www.angelfire.com/wi/jettech/

Joe