The original story of the genre is "Killdozer", by Theodore Sturgeon. (Great story, btw.) In the story, the protagonists were trapped on an island...
Hulking Size (duh), Superhuman Strength, Stamina, Toughness and Speed (at least). Catch should fit your story needs; possibly 'Holy Stuff' or something more obscure...
Fists (for ramming), Alertness, Athletics, Endurance... Other than Intimidation, no real need for social skills...
Aspects: Freaking Huge, I'm a Semi!, Unstoppable, I Fear Nothing...
Some really nasty spirit/demon from the Never-Never (not fae; too much iron).
The above is tough, armored, regenerates, can absorb consequences, and should be a fearsome-enough opponent. But it's not that smart or manueverable, so it can be tricked.
As for guidelines; whatever makes a dramatic story. If your players can steal a cement truck and manage to make the rolls to ram (don't make it easy for them to get to a construction site or the truck; the kill-semi isn't a genius, but it could figure out what they might be looking for and try to cut them off) maybe it works...or maybe the semi, battered but still functional comes rumbling out of the debris field... At a guess, a speeding truck would be a weapon:4
Hope this helps...