I have two Fursuit type costumes (rabbit and a dinosaur ) that I need to repair this week. The head structure under the fur (some sort of very thin plastic) is  literally falling apart. I have no clue what to do. My first thought is to use white duct tape to stabilize the plastic. Any other suggestions, tips, do's n don'ts?  Thanks!

You might want to try Wonderflex. http://www.wonderflexworld.com/ You might be able to repair the broken areas with it.

Personally what I would do is strip them of the fur or fabric covering and then make a pattern of the shell using the tape up method we have talked about here before. Then you would have a pattern you could use to make a brand new shell out of EVA high density foam. The old shell I would bet is going to continue to degrade so patching might just be a stop gap measure.