I've read that kitty litter in tights is good.
Do i need to be wearing the tights at the time?
Basically what you need to be doing is killing off the bacteria causing the smell, or else the smell will just come back after you have filled them with kitty litter or whatever.
When boots are not being worn they shouldn't be in the bottom of a pack where they were put sweaty and warm and foisty from the day before. leave them somewhere where they can get some air and sunlight to them so the moisture can leave them.
I've heard tea tree oil can help too, it's a natural antiseptic. And putting them in the freezer to kill of bacteria.