Today I started with the first Titan-Killer weapon - the Vulcan Mega Bolter :)
A "heavy 15" weapon with 60' range
It will be mounted centrally, with limited elevation, and no traverse.
It is low and back enough to not limit the two Vanquishers field of fire.
Snugs in nicely.
Next things up is more detailing, the actual mount and then the Ammo Feed.
The idea is to have two huge Ammo Drums on the inside, right behind the two Vanquishers and an outside Ammo-Feed leading to the Mega-Bolter.