That looks great man. I love Nam dios
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I agree that the helmets look a little to tan. Some did have a tanner look to them, but I'd add more splotches to the helmets. Maybe have some more tan looking and some greener looking. The helmet camo pattern was called "wine leaf" and was reversible. Here are the patterns.
Here’s the same pattern, only grayer in color (due to just natural wear, or just different colors on the pattern).
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This is the reverse side, which has an entirely different pattern.
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As for the sandbags, they probably would have just filled them with that red clay material around there in real life. I’d add some of that red clay oozing out. Don’t put a whole lot though since it sticks a lot. As for vegetation, you could add some, or just leave it as is. On firebases, it was mostly mud from trampling anyway. It’s personal preference if you want to add a blade of grass here, or there. Just curious, but what set did you use for these? It looks like a Dragon kit with Verlinden heads.