Have a peek at http://www.polypipeinc.com/ for some plastic gas pipe, also over here more and more new homes (all price ranges) are being piped with PEX for the domestic water piping, a plumbing company friend tells me that this stuff is just as reliable as copper, the quality of the installation is what determines the end result. I am not in the trade, but am involved with some combustion research, and we did test some PVC pipe as the premix feeder into a ceramic burner head and I was very surprised that the pipe performed as well as our metal premix pipe. Of course, there was no flame impingement (the burner head is isolated from direct contact with the premix pipe) in either case, so the carrier pipe itself is at normal room or outside temperatures. All materials have their place; safety, longevity, maintenance and cost effectiveness are what is driving our combustion experiments. Thanks all for the interesting comments...