We put in a GroundZero after moving here. It look like the one in the previous photo and it's in the small side of our 3 car garage. We have been perfectly satisfied with it but it was not my first choice. I wanted an outdoor one in the back yard. It would have been about $1K less expensive at that time but that's not the reason I wanted it. I don't think I would want to be in ours if there was a house or car fire just above it. The wife always wins out, of course.
I've often thought of a damaged car with a leaking fuel tank above me, but at the same time - running outside with my wife and two terrified kids in golf-ball sized hail and driving rain, with the potential (if you're alerted late) of glass, sheet metal, etc., blowing around at EF3 speeds wouldn't work, either. This way we stay high & dry on the way to the shelter. If it's apparent that we'll actually need to use it, the car is going out anyway; let the 'nado have it. I think you made the right choice.