Careful with Squadron Green Putty as it contains Toluene and melts plastic in a similar way as Plastic Model Glue. Not suitable for sculpting at all. Just seconding MrBestor.
To be honest I was skeptical about green stuff but now that I have used it a few times for sculpting minor bits, it is actually really easy to work with once you get the hang of it (which did not take long),
IMO. Just check out the tutorials on DakkaDakka for pointers and try it out.