I'd try storing them long term, see how the fluid breaks down the plastic. And maybe give them a little squeeze, a shake, then another squeeze, every day. In three months, we'll check on it's packability.

For this kind of thing, I rather like a glass bio-specimen or perfume vial. They are made to handle this kind of thing, and the heavy duty borosilicate glass lab vials can take a LOT of abuse. I've had them trapped between my boot and tile, and they didn't break.