Always before I've used car filler which had the virtue of being cheap but can't really be applied to miniatures.
Now I've found something that can.
This is Vallejo putty. It's basically plastic in a load of poly cement. All you do it squeeze it out
Smooth it down
And then sand it.
This is will work on large plastic miniatures as well; it will also be a lot cheaper than greenstuff, I think. It's also got some fairly
Obvious possibilities for terrain and dioramas. Next set of plastic miniatures or conversions I use I'll give it a try and report back.