I tried this recently and it has worked reasonably well me so far, although I have only molded a few. I was looking for the most inexpensive way to mold my own soft plastics and that is what I came up with. I bought some POP from wally world. Built a cardboard box about 12 x 6 inches using strips of cardboard taped together with duck tape. Lined the inside with aluminum foil, greased the worm I was using as a model with a thin coat of vaseline, placed it in the bottom of the box with the flat side of the worm facing down (cant make completely round worms this way). The vaseline helps hold it in place while the plaster is being poured over it. Mix the POP, pour it into the box enough to cover the model worm about an inch deep. When the plaster is set turn the box upside down, remove the foil and model worm from the plaster. Go back to Wally world or if you're smarter than me just pick up a can of heat resistant car engine paint at the same time you buy your POP. Paint the mold and let it dry completely. The paint helps keep the plastic from sticking when it dries in the mold. You can also use a small amount of vegetable oil in the mold if you desire. I have a ton of old plastics that were battle scarred and too beaten up to use again but I never throw them in the water for fear a fish my swallow them and die so what I do is melt them down in a gravy pan or any pan with a spout over no higher than medium heat. When the plastic is liquid I pour it in the mold, let it cool, remove it, cool it in a pan of cool water, and trim it up with a utility razor blade. Like I said this is a very elementary way of doing it but it is also the cheapest way if all you want is a few worms at a time and you are just looking for something to do with all your old scrap plastic. One tip is dont try to mix colors always melt the same color plastics together. If you want multi colored worms melt the colors in seperate pans. You can also make custom molds this way by using different parts from seperate worms as your model. I made a worm with a craw claw at the tail and three tenacles coming out each side. I caught a three pound spot on it a couple weeks ago so I know it works.