JohnnyG,
I replaced our vent in the kitchen area with a Fatastic Fan. I had to build up the area on the roof under the flange on the Fantastic so the fan does not extend below the ceiling. If it extends more than 1/2' inch or so below the ceiling the shell will not close and you could damage the roof and the fan.
I used some 11/4" thick molding I had lying around to get the desired height. I screwed the molding to the roof (be sure to countersink the screws), and then screwed the fan to the molding. Use white silicone caulk or rubberized caulk sold for use on aluminum roof installations to seal everything.
I used the existing wiring for the light to run the fan and everything works great. It is handy for pulling out cooking odors and heat and is pretty effective for cooling off the interior at night.
Bruce Martin