So sorry, white rot is a proper b., isn't it. I've given up with everything except garlic which is in a big bucket, and chives which are not affected. I know onions and leeks are cheap, but it's not the same as growing your own, I used to love growing onions with the ritual of bending all the stems at precisely the same angle, the woggling to see which were ready, the tying them up in old tights...
Have you tried the garlic watering method? That worked one year for me but the rot was too much subsequently.