I agree with Craig, I seriously wouldn't leave my car at M'popo as they are not the "tap in the little back window and unlock the car and rifle through the glovebox" type people they are like human keas - they will rip everything apart and then take a dump on it as well (they eat a bit better than keas so it's pretty messy). 

Probably stating the obvious but even though it's a popular tramp it is across a mountain that catches all the sh1t weather and there's no shelter en route.  If it is horrible weather and you're not following poles and millions of footprints your probably off route. 

 Also worth noting the hotpools at Ketetahi are on private land and trampers shouldn't visit them otherwise track access might get closed (as the track crosses private land).