I need to do one on my Berlin king tiger... any advice?
You can try brush painting it...probably done on the real tank if it was hard edge cam.
Or you can use Tamiya masking tape to mask the hard edge and then airbrush the cam colours.
Or you can use "Blu Tack" or "Fun Tack". Just roll it out and apply on the model and then airbrush the cam colour. It peels off very easily and can maked multiple angles. It goes by many names:
Or you can use "Silly Putty" the same way as Blu Tack.