For those interested in canning them via the water bath method for long-term storage, note that there's a significant tradeoff: They will store longer, yes. But they will also lose a lot of their "crunch", which is a huge part of their enjoyability. For the best results simply pack the onions in jars and pour the hot vinegar over them; the heat from the vinegar is usually sufficient to create a vacuum as it cools seal the lids (a seal adequate for a few weeks' storage at room temp during the maturation period while the flavors are developing). At the conclusion of the maturation period and once opened, store them in the fridge where they will keep for 3+ months.