Once I left some unleaded gas (with ethanol according to pump) inside a brunton bottle, in two days time the plastic cap (including threads) became soft enough I can easily make impressions with my fingernail, freaked me out and I've been extremely wary of gasoline since.

With kerosene it has been over two months without problem. Although kerosene isn't good for simmering from my experience, turn it down too much and there isn't enough heat feedback to vaporize (the type of generator that pass though flame may fare better).