I should point out that moth crystals are recommended for winter storage not killing off moths. No doubt it would kill them though. Place empty boxes & frames inside plastic bags with moth crystals for storage. I do not use plastic or chemicals. I make 100% sure empty hive boxes are moth free before winter storage then block the entrances with duct tape &/or pieces of wood. Freezing will kill them. They will vacate the hives on their own if left open & exposed outdoors. They like dark cramped places. Moths generally will not be present unless the colony has other serious problems & is all but dead. Consider them as the undertakers who finish the job. They will ruin the wax & eat the wood too.
Moth crystals' active ingredient is paradichlorobenzene while moth balls are made with naphthalene. You could probably research these chemicals and see why the crystals are better for honey supers. I have been told many times that bees will not return to supers that were stored under mothballs.
Argue for your limitations and they are yours forever.