Welcome to Librarium Online!
Erm... you short on cash? Otherwise just buy the thing, it looks absolutely sexy. I might just get one for a showcase, along with Be'Lakor, Valten, Archaon......
If you can't buy one, I'd just get some kinda container to be the barrel, balsa wood carrige, with bitz and greenstuff where needed. Oh, and you'll need some dwarves to convert into crewmen.
Well a truckload of plastic skulls fo the barel may be useful as well as generaly anything from the Chaos plastics range particulary the chaos space marine vehacle accesory sprues
Ask not the ruleboys a question for they shall give you three answers each true and terrifying to behold
Have the chaos dwarves shovelling zonbie corpses into the back as ammunition.