It's been a few years, but last time I bought an extract kit from them the liquid extract came in a screw-top plastic bottle. It might not be a long-term shelf stable sort of thing, but their customer support is super knowledgeable and really helpful, so you can always give them a call or chat with them online to find out.
I did something similar once and have several sealed cans of LME on hand in case of a "brewing emergency". One of them ended up being Maris Otter, and every time I look at that can I think I should use it. Then I just go buy grain instead. Go figure....