http://www.vodoskok.hr/prodajni-program/sustavi-opskrbe-prirodnim-plinom/cijevi-za-opskrbu-prirodnim-plinom/
exact inner diameter outside diameter is slightly larger ie twice thicker than your specifications it should not be a problem By the way you have room for cover mounting that is another plus
This company is in my country but the it does not matter plastic gas pipes should be the same all over the world
so find an acquaintance someone who works on construction field If you ask nicely they'll surely give you a piece of pipe
i was able to show how much the human interference messes with capacitance. its not extreme enough that if you have things spreed out from where your working, you should be ok... ??
see around 49 min.
https://www.youtube.com/watch?v=PBtbj6kzzHA
~Russ