My traitor forces have a well equipped gun line specialising in siege warfare. A large part of the artillery force includes Bombards.
The Bombard comes in 2 different flavours, one based on the Chimera chassis and the other on the Leman Russ. I prefer the Leman Russ variant, the heavier chassis seems to suit the massive siege gun much better.
MKHAND_INDUSTRIES again, I chose the option with a separate loading arm to make clean up and painting easier.
Given the size of the shells these things will fire, some Trojan ammunition transports and trailers will definitely be needed soon. There is no room for the crew other than a driver, some additional Chimeras or Centaurs will also need to be printed.