I suppose pictures would help, but I repair a fair amount of plastics on cars/trucks and I use a tool that heats up metal "Stitches" that are applied into the plastic across the breaks. Before I bought the actual tool, I'd buy the stitches, hold with needle nose pliers, and heat them with a torch, then dig them in while hot. After a few, you get a good idea how much heat to add for your particular project. There are adhesives that might work, but I've not worked with any that held up structurally speaking.