Nice looking model. A good finish on it.
Most people ask for painting advice before they paint.....just sayin'....this IS a modeling forum...
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Anyhoo..the "wooden box", I assume, if the jack block on the side by the spare wheels storage? Usually these would have been painted along with the rest of the tank, but a lot of guys paint them in wood color, or better yet, substitute a piece of real wood for realism. So you can go either way on it, for artistic license.