Cheese1 -- I bought the "kit" at Camping World and believe it's made by Phoenix. I coaxed R-Vision to fax me the roof and both side wall blue prints of the rig to make sure I knew in advance what I was cutting into. Used that info in locating the roof ribs for installing the Yakima box as well as the outside shower.
Gene -- I routinely get 11+ MPG driving at and above the speed limit (80 in a 75 zone is comfortable). What speeds and driving styles are you holding to to get such incredible mileage?