Check out West Systems G-Flex epoxy. They have a video where they cut a plastic kayak in half and then "glue" it back together. I've used West 105 epoxy for years building small boats and canoes. The G-flex is new formulated for roto-molded plastics. I've used it for small projects. I picked up a guart last week from West Marine (a different company that sells West Systems), it's expensive. I hope to fix some cracks in shower pan and other ABS parts in the next few weeks.