I had a couple of games against a WE army last weekend, and under the Call to Arms comp, I decided I would try and play with five warmachines (without a Master Engineer). Specifically... Two Grudge Throwers with Accuracy, one with one pen rune (one with burning as well), and the other with two. Two Organ Guns, and a cannon with forging (and maybe burning) all with Engineers besides the Organ guns.
Now against WE's this worked really well, the first game I never miss-fired so that was a bonus, but the second game still saw them as M.V.P of my army. Tress don't like fire. Now when it comes to five warmachines and really only four blocks to protect them, one with scout so I the Rangers might not always be there to cover a flank.