I really like these things. I showed them to my buddy who plays Orks, and he hit the roof. I may have to help him scratch build one or two for himself. (as I am the better scratch builder of us two) I also love that your orks are not necessarily green. I have always thought that if I were to start an Ork army, I'd make them purple!
I also love the dirt detailing you throw in there on the treads. It really sells the look.