Glass containers with plastic lids seems best. I have had HDPE plastic containers crack and leak out MMS (22.4% / 25% NaCLO2). I would fill glass containers almost full to reduce air as much as possible, yet not allow MMS to contact the plastic lid. Do label each container along with the date bottled.
Have read that MMS will keep about 5 years if kept cool and in a dark place.
You could sell some of your life-time supply of MMS.
Eye and skin protection is always a good idea when handling chemicals. If you spill any MMS, wipe it up with a wet cloth or sponge and rinse those with water. If spilled MMS drys into a powder, that would not be good.