A question on rubber seals....

[Doddsie]

Greetings All,
My friend has made a still with an old canteen boiler, and has been struggling to seal the top of it and was asking me if I knew if using a rubber seal would work. We know that plastics holds a lot of leechers and crap but does is that the same for rubber. I did mention cork to him but the flang is really to small to apply any cork. He has managed to seal the boiler with the rubber gasket but is just a little worried that it may react with the vapour???.

Thanks for all your help before hand Doddsie.