I just bought a thermos-type bottle with a freezable insert that supposedly keeps 2 MJ pens with awkward shapes cool for about 72 hours. Havent tried it yet. A wireless temperature probe will go in there so I can measure how cold it stays over time. Should it miss the advertised performance, I return it! Soft cases with little freezable gel pads exist too, but their reviews are very mixed, with some saying the frozen gel pads thaw very quickly and dont hold a cool temp. My vote goes to a vacuum flask, thermos style, though its bulkier.