You can use glass (it looks much better), but then you have to assure that the temperature does not go over 30 C for prolonged time. I store mine in a small glass vial, as a solid lump. Even if the temperature rises to over 30 C for a day or so, it will not melt at once. All this heat also has to penetrate the metal lump and it takes time. So, if you store your gallium in a glass container, and the lump loosely fits in the container, then I would not worry about cracking of the container.