I had a regulator on firewall, was told to move it, its now on my down bar to front of frame. brian answered your question correct. If you had a hatch back car or a wagon or a blazer, that is open like I do then you have to do things to make it legal, also if fuel cell is hanging low out of trunk, you have to build a sheild around bottom of it, unless it is aluminum, which is what I have to be legal