I have based a couple of Looted Great Cannon (that I use as Rock Lobbers in my Age of Sigmar Pirate Orruks army). Their gun carriages are made from Orruk Chariots. They have been in my army for years but I have only just got round to making bases for them. They always looked a bit lost without bases so I'm much happier with them now!
The timbers on their bases are chopped up Goblin Town floors (originally from the "Escape from Goblin Town" starter set for The Hobbit) with some added skulls from the awesome "Citadel Skulls" box.
These two are added to the smaller one I based in 2016 (!). The gun carriage for this one was made form cut up Screaming Bell timbers (left over from another project).
Update (09/01/2017) now with gun-crews!