On my Isuzu Rodeo it was under the driver's seat. Saab Viggen it's in the rear hatch area. 1993 Isuzu Trooper was under the driver's seat. Subaru SVX has it in the trunk under a false floor. On my friend's two Explorers we put it under the passenger side rear bench. Another friend with a Saab 900 put it in the rear hatch area. Same thing with another friend and his Saab 9000.

I guess I/we put it wherever it fits best as far as being out of the way and still being able to access the controls go.