snail stop (or any other bait, sold in home depot) did the trick for me.
i add the bait to the floor, (pleny of them) and wait , check floor next day, i killed dozens of those suckers , and it seems i am clean , however i do recommend doing the same thing once every two week for 2 months, and you will get rid of them forever, (given that no other infected plant either with snails or slugs enters the greenhouse (eggs).