Sounds like a fun little project
There are two ways I could see you going for this, using normal Tau with some sort of tunnelling tank, a Tauish mole machine if you will. So you'd have to loot a tank, and give it some method of moving underground. At the very least a tau pirhana for the cockpit, with a drill assembly on the front.
Or go for a tau allies sort of thing, using kroot (or even stigwigs) and some sort of converted monster, like a giant kroot ox. Might take a bit of work, or finding a good model to base it off of.
Anyway, just a couple of ideas of places you could go, let us know how the competition goes, it sounds fun!
It's all in the name.
Looking for a club in Brisbane, Australia
? Come and enjoy a game and a beer at our friendly club in a pub at the Centenary Tavern, Sunday nights from 6:30. All brisbanites welcome, don't wait, check out our Club Page on Facebook
for details or to organize a game. We play all sorts of board and war games, so hit us up if you're interested.