Sorry I missed this somehow. I just checked it. The measurements are really from below. Once you remove the headliner you drill up through the roof where the dual layer starts and make sure you leave the space from the front crossmember forward. There is a good youtube video. search for Mory inc Raised Roof Van Top Conversion Cutting out the Roof. Sportsmobile forum won't let me post the link. I used Sikaflex 221 to seal it along with some sheet metal screws and some J bolts just for some extra piece of mind.