I have to agree with Kyle and Eric: I've found the Great stuff made for windows (it's more flexible than the other stuff) is a great cheap alternative to a new insert or the more expensive repair kits. Wrap the target in celophane, poke a small hole in it for the nozzle, fill up "most" of the cavity. Remember, this stuff expands so you don't need to jam it full or it will spill out the seams. With a little practice you'll get the hang of it. A can of cheap spray paint in the general color of the animal and you are in business.
And yeah Eric, that is a pretty nice setup.