I feel like whenever you're putting that many points in a single war engine (be it a Lord of Skulls, a Brass Scorpion, a titan of some sort--whatever), you might as well also take Be'lakor to cast Invisibility on it... (where to find the points for the fellow, that's the real question).
I feel like an ADL wouldn't be amiss, so that those Horrors/Heralds could go to ground for a rerollable 2+ cover save while they're summoning.
What sphinx of plascrete and adamantium bashed open their skulls and ate up their brains and imagination? Imperator! Imperator!