Thanks all for your comments.

I think this idea's worth it.
I was actually thinking, after seeing Avatar, that I'd use the giant bulldozer that they smash the cameras on, as a battlewagon.
One trukk would definitely be a devilfish, as our fluff is that the Tau are trying to keep the Orks bottled up in the mines.
The mine carts idea has already been suggested by several people, so I will definitely be doing it. I'm thinking the mine carts themselves will be warbikers, and the warbiker boss will have the little square train engine, as he is the leader. The engine will be properly souped up to a deafening roar, as per usual.
The overalls idea, I like. I've never thought about that before. Should they have white shirts too?
As for the buggies, I was thinking they'd be the trucks that would have picked up the coal from the mines.
I'm thinking that the Orks themselves aren't mining anything(i don't think that coordination is in them really) but the moon above my
IG planet is a mining base, and the orks just started raiding there. And since the miners were the only ones tough enough to stay alive after they'd killed the PDF and civilians, the orks started donning their gear as trophies. The mining helmets are a prized commodity among my orks
EDIT- Also, I was just thinking about my nobz all having big choppas, and giving them all two-handed picks, and then maybe giving one of them a fake beard to tease my dwarf buddy

what do y'all think?