I do huge numbers of skins every year and have found some big errors the hard way.
Do not use salt to preserve skins except when tanning and then rinse them very well before using in tying! residual salt will rust hooks in the blink of an eye in a damp fly box. Think saltwood Brownings...
Freezing does not kill bugs, if it did there would be none in say central AK where it routinely goes well below zero! Wash in warm, soapy water with a capful of bleach. Everything bad dies quickly in bleach. Rinse well and blow dry if doing just a small number. Finish by dusting them with borax while the skin is still slightly damp. If you have a bunch toss them in a bucket half full of dry sawdust and borax. Rig up something to roll the bucket slowly to dry and polish the feathers/fur.
I have tanned lots of squirrels in battery acid, salt and water. Rub Neatsfoot oil into the leather while working them to dry.
Lots of differences in the leather thickness of small critters. Some rabbits are too thick to be useful for flies unless thinned. Varying hares are mostly too thin.
