PTFE would be very bad because it creeps horribly, even a moderate stress and room temperature.
Many plastics would perform properly at +120°C and that little pressure. Don't overkill because heat resistance is what makes plastics expensive - and they can be VERY expensive. Have a look at Matweb and Goodfellow for instance, or better, at plastic manufacturers.
One other solution is just glass. Some chemistry labs still have a craftsman capable of manufacturing any shape - or choose among existing hardware, for instance at a chemistry provider, as you'll probably find an acceptable shape among the many existing ones. With some wall thickness, 17b is easy to withstand.
Carbon fibres conduct electricity. Glass fibres would not but their resin isn't very inert and may react with you gas.