Really easy bronze:
Prime black
Base coat tin bitz
Wash with thinned turquoise or a green
Drybrush with bronze
Edge highlight with bright brass or gold
For tanks, too much metallic can look really gaudy. I would use your trim color as the dominant color and use bronze on insets and trim. Alternately, use bronze, but dirty it up alot with washes and stippled corrosion, mud, and gore which will dull down the overall effect.
This is a really good example of weathered metal:
http://coolminiornot.com/166293
More iron than bronze (iron oxidizes to yellow or orange whereas bronze, being a copper alloy, patinas green), but gives you an idea.
Black would make a good trim color with bronze. Kind of the inverse of the Black Legion colors.
Here is another example with black weathered metal:
http://coolminiornot.com/75643