Use a 50/50 mix of Greenstuff and Miliput. Effectively it's a 4 part putty but it works great. It gives you the best properties of both products with none of the drawbacks. It's very easy to use and cures to a good hardness that is very east to cut, file and sand. Heat will help speed the curing process, but don't use heat with plastic figures/components or else they will warp.