Wow, it's been a while...
The picture below was my first cut at a Colossus Siege Mortar, very quick and dirty completed in the morning before a tournament. Kind of loosely based on the Morser Karl Gerat.
I built the main body of the mortar based on the paper-craft, the breach section and the barrel are plumbing fittings. I added a pair of recoil dampeners made from tubing and some bits from Sentinel kits. The mounts are just bits of plastic tubing and a plasticard plate as a base. The muzzle and breech are courtesy of the plumbing section of the local hardware store.
And here's the finished product, ready to rain death on the battlefield.