So I'm converting my old Armorcast Shadowsword to be a Chaos Shadowsword as well as a Khorne Tower of Skulls for Apocalypse. I've got Thunderfire cannons to be the Doomfire Cannons, but I'm unsatisfied with the ideas I've gotten for the Skullfire cannons mounted in the tower. Just using plastic tubing is one answer, but didn't know if some of you out there had more creative (and much more interesting) ideas.