I tried to emphasise the rounded M4A1 cast-hulls with a double-highlight: an intermediate , just slightly lighter highlight, then a more confined, lighter highlight painted within the previous. It looks OK representing a softer edge without too much extra work (they're enough as it is!).
Rear deck view: lots of clutter and stowage added in addition to the pre-moulded resin bits. The painting thereof adds a fair bit more time but is probably worth it.