Hi Ralph,
I'm not to sure about the armor, but I might be able to help with the mud.
If you use any type of powders for finishing your models try this;
Put a little of some darker color or mud color, (Your preference) on a piece of paper, wet your brush with water, mix in the powder with the brush and use this to add to the cracks and such on your wheels. After it drys it stays put better and and gives it that built up look. You'll have to try a few times before you get the desired look.
This site explains it better,
MIG Powders Good luck,
Bob