My two cents worth:
I have been fishing with plastic baits since the late 60's. Most places packed them in a small amount of worm oil to keep them from sticking together and to keep them from hardening. I always kept some worm oil on my worms in their double sided tackle box. Yes it leaked a little, but the worms were always fresh and supple. I still pack the soft plastic baits that I make in worm oil.
Salt washes off, the oil washes off, so what is the best to keep your worms in?? My money is on the oil.