Putty; generally used as a body filling agent in holes, works especially great as a sculpting medium.  It globs on thick like tooth paste, dries in about 5 minutes, is easily sand-able, can have more putty added onto it, and is a very strong material when dry.  Plus, you don’t have to worry about leaving finger prints or deforming a finished section like using clay.  So, I sculpted the entire Master Sword handle out of body putty with steel inside as the base.  I did recently start using Sculpy though, which does work very well too.  Doesn’t smell as bad either.
            So all you really do here is mass on the putty into the approximate shape, and then sand away; adding and subtracting as you need.  A lot of the skill here is sculpting, and not really technical know how.  Once done, prime and paint.