Using the DaVinci tank is a brilliant idea; thanks for the suggestion Tordenskjold, if I don't manage to build one myself, I'll be ordering one of those for sure.
Craig's idea for decoration is inspired; I hadn't given any thought to that at all. Now I'm thinking that the crew could build a dragon or Fu dog, like the ones used in chinese dragon dances, on to the outside to make their snail more fearsome. Time to google fu some cheap plastic ornaments to convert.
I had planned to have a sorcerer amongst the crew to use Zone of Shadows to protect their aproach; perhaps Dragon Breath would be a good investment too.