I pickle shallots (do you call them that?) in the UK just using spiced vinegar. However I keep them in a net bag in a dry place for about three months before I pickle them. This takes a lot of water out of them and allows for a better absorption of the vinegar. They stay nice and crisp for about two years and are not too bad at three years, Some people leave them to soak in a strong brine (sodium chloride/salt) solution over night instead as this also removes some of the water. Trying them both together might put some of the water back in.
Bigal (UK)