That tutoial is good but try to use grease proof paper and roll some warm greenstuff otherwise it can be too hard and try to add the folds as they would occur naturally
If the greenstuff is still soft enough it will actually bend to the shape you want it, but you will still need to sculpt it into shape.
Try it first on a spare guardian or something, its not too hard you'll get the hang on it in one or 2 go's.
btw, thats looking really good so far, be sure to post it up when its finished, thats really clean and smooth looking white, good show!
hope it helps