Warhammer needs more steampunk. For the base I covered the whole thing with epoxy plastic and rolled the metal wheel treads through it to leave tracks on the ground. It started as a Doomwheel in my Skaven army. When they changed the rules, I converted it to be a Lightning Cannon.
Here’s my nickel’s worth of free advice on epoxy plastic. You can get Greenstuff from Warhammer or Sculpting Putty from Reaper. But the truth is, it’s not much better than the tubes of quick dry plastic epoxy you can get at any home store in much larger quantites and a whole lot cheaper. They have quick dry wood patch, quick dry metal patch, and even underwater repair patch. All it changes is the dry time. The slowest dry time is best for custom work.