I don't know anything about weathering kits but techniques, the kit comes from your standard hobby kit. You can try chipped paint, oil stains, rain/dust marks, etc. The link below is the best source I can priovide regarding armor weathering.
http://www.missing-lynx.com/rareworld.htm
I've tryed my self the rain marks technique shown there and works great!
Hope this works and good luck!