Basically i was taking the fantasy approach and decided to mount the treb on a massive "war of the worlds/Half life 2" type walker...steam powered of course! the little cube on the left hand platform represents the size of the pilot.
The idea was to have it all IK'ed up and use spring dynamics so that when it launched a missile it would sway back and forth with the inertia. The catapult itself is all dynamic, with the release keyed. I've just tarted it up slightly by parenting some other geometry so as not to mess with the dynamics which is set on the proxy models.
good luck to everyone with the challenge.