Basically I got tired of some of my newer Enthusiast FOV vehicles and older Action Grade ones looking like they just drove out of the factory, so I decided to weather them. My goal was to make them look more like my older, heavily weathered FOV Enthusiast vehicles like the first-series T-34, Jagdpanther, etc. It was a fairly simple process: lightly spray the underside and sides with a light brown color like Tamiya Flat Earth, then dab on a darker brown to simulate mud and splatter using a color like Tamiya Red Brown. Detailing could be done in a variety of ways to simulate scrapes, chipping, highlight bullet holes, etc.
Here are some pictures of my first three vehicles, including some "before" shots of the item in stock condition. Let me know what you think

Panzer IVG Tank:

It helped to already have simulated mud tooled onto this model, though Unimax left it unpainted on the stock version.

Sherman Firefly Tank:

(Those are the rare 21c British Paratrooper figures with the Sherman


M5 Stuart Tank:


This is the Enthusiast version of the FOV Stuart - mine was an unweathered Action Grade version I got a few years ago at Target.