Hi.
I use a fine brush and Humbrol matt 34 as the new formular seems to be more translucente than the older stock was which in this case is a good thing. I tend to apply a small blob of paint and then drag it in the direction of gravity, its easyer to do than tell lol. As with all things practise is the key. My insiration is "The Art of Weathering" Martin Welch, published by Wild Swan. I'm sorry I have no examples on hand to show you my railway modeling is on hold atm and my stock is completly inacsessable although I'm doing some millitary stuff Tanks don't tend to be steam powered so thats not much help.
I hope that helps regards Lez.Z.