I don't even know if mine has a metal or plastic body. I'll have to check.
About evaporation : I guess if the gasket around the "match" is good, you won't have any or at least not a lot ...
I forget my "permanent match" in the glove box (?) of my car for over 6 months.
When I re-discovered it, it lighted allright, there still was enough fue inside.


Alain