Don't know "Weld-On #3", but I presume that it's fairly volatile. I have found that, even through an Australian summer, keeping such substances in the refrigerator (tightly sealed, naturally!) generally prevents evaporation. I've kept MEK-based adhesives quite successfully in the fridge for several years at a stretch - there's still a bottle in there that I brought up from Sydney six years ago, and it appears not to have lost any contents at all.