If I have to keep seeds for less than a year, I keep them in the fridge, making sure they are dry and not in contact with any moisture. If I need to keep them for more than a year, I freeze them (-22C/-7,6F). I have seeds that are 8 years old in the freezer and the germination rate is almost 100%. Make sure they are dry and it should be fine.
Personally, I prefer to let the jiffy plugs dry a little bit so I can add fresh water from time to time (fresh oxygen) but it can be tricky so I don't recommend it if you don't have time to check on your plugs several times a day. If you keep the lid on the Tupperware, it's fine as long as you allow your plugs to "breath" once or twice a day. If you smell mushrooms when you open the Tupperware, let your plugs dry a little. Jiffy are wonderful for germination, I can't do without them anymore.
Kudos, mate and good luck for your grow.