vocab question

You can say 困/kun4 to refer to be stuck or trapped, but I don't think Chinese people really say "我希望你不要被困在电梯里” as the translation of "I hope you don't get trapped in the elevator!", unless the speaker has some evil mind with mocking tones or something like that. It sounds weird to Chinese people.

Right, so what do they say?

For a warning to your Chinese freinds stepping into a very old elevator, you can say 你乘电梯时当心点 or 乘电梯时小心点. I think people will thank for your warm heart.