ALAN - I have been guilty of NOT commenting on your build lately but I read them all). You sort of lost me on the wash for the tank - going to have to study that a little slower.
That's one of the reasons I like this company's kits Sherrel! His methods are different, but not necessarily more difficult. The chalks I speak of are Rembrandt chalk sticks. You shave off what you need with a single edged razor blade. For that tank, I used three rust shades. They apply with a very soft bristled brush. a stiff bristled brush will leave brush streaks, which you don't want! Get the chalk on the tank, then I used a different brush that I dipped in plain alcohol and touched to the upper rim of the tank. The alcohol runs down the side of the tank so you get streaks and patterns like rain washing crud down the sides and rust starting. Do the whole thing again with three colors of brown. He tells you which ones in the manual and I won't repeat them here because the Rembrandt colors are all identified by number and would be meaningless. The alcohol has to completely dry between each step. after you've done the rusts and the browns, you add more dry chalk until you like how it looks. His methods for weathering resin castings give really neat effects. There's a short video on his website that shows you how to do this stuff. See it here. It's just a couple of minutes long.