Actually, you can store filled cartos for a pretty long time with the condoms on them. You don't think those pre-filled cartos you buy were just filled the other day, do you? PG is anti-bacterial. Any critters would have a difficult time in a PG soaked environment. PG and VG also attract moisture, so they don't dry out or get thick and gummy. In fact, if you leave a container of PG out in the open, it will increase in volume because it will suck water out of the air just like it sucks water out of your mucous membranes. In a carto, the VG and PG will keep the flavorings from drying out as well.
You can fill a new carto, seal it back up with the condoms, (to prevent leaking, moisture intrusion and contaminants, not to keep it from drying out) and it will be good for as long as juice would stay good in it's bottle. Store it the same way you'd store juice in a bottle, out of heat mainly since, in a carto, light is not an issue.