For a buck, ninety-nine you could get this app if you have an iPhone.
It's by Steven Eppler and app is called Tiltometer - Off Road.
You can orient it simply by mounting the iPhone, starting the app and hitting the orientation cross-hairs button. Whatever the attitude of the iPhone the app will orient itself, vertically, horizontally, canted, whatever.
The app has two warning settings, one at 30 degrees where the background goes yellow, and one at 45 degrees where it goes red and an audible alarm sounds. Perhaps Steven can mod it to say, "Danger, Will Robinson!" or Hans Solo's voice, "I've got a bad feeling about this."
Edit: The app has a compass and altimeter as well, and has a night vision setting.
The app allows a limited number of vehicle choices, though, sadly, no generation of Montero is available.