I was browsing the Forge World web store when I found the Mechanicum Krios Battle Tank.
The more I looked at it, the more I thought that this would make a wonderful steampunk or Victorian Science Fiction heavy artillery piece. You could quite easily imagine a British artillery crew preparing to fire this on the surface of Mars. You would need to replace the Mechnicum crew and the icon on the back of the tank, but not a huge amount of work.
Only downside, it is £81.