I agree on the Aves putty. I had used Milliput for years before a taxidermist friend gave me a sample pack of Aves to play with. Very easy to work with, smooths out with water, and easy to sand.
If you get stuck having to buy supplies from Wally World, check the plumbing section for the epoxy putty. It's a lot easier to work with than JB Weld!