Well, after reading your post about dioramas, i guess the AM way is out of the question.
First, the basic pattern will depend on the tank.
For a panzer IV (or one of it's derivitives), i had some sheet styrene that had small grooves cut in (sorry, i forget what it is called. Something for like HO scale buildings). I cut off a small strip as a spatula. With squadron green or white putty, i applied it to the areas that would have it. Every quarter inch or so give it a little wave to represent the vertical break.
The first time i tried it came out pretty well. At least i was satisfied.
Here is what it looks like.
Stug IV Oh. You should post this question in the armor forum. You will probably get more replies.