basically you just have to think backwards on the weathering.
you paint the first layer and then brush on latex "Art Masking fluid" is the official name if you were to go ask for it at the craft store.
then you paint on your second layer color, and expand on the current masking locations or add new ones.
Then paint the top coat. once it dries you need to use something to scrape the latex off with. i used the plastic clay sculpting tools. and it makes a MESS so make sure you do it outside or something. (you could do as many layers as you want but for this one i just did the 3 pictured and then the markings)
id be happy to help with any other questions, its really not that difficult, but im glad all of you like it !!