PastorGary - that's great, thank you! when i was thinking of how to mount the antenna to the very top of the tire carrier, i was trying to picture how to do it using some sheet metal and maybe some really thick washers. i never thought of a flange - i think it'll fit perfectly, and is exactly how i was picturing to make it! the top is triangular and the sides measure 4.5" on two sides and 5.5" on the other. even better is that there are already 3 holes through the top, about 7/16". i traced it out on paper yesterday, and will take that to some hardware stores. if i'm lucky enough, i might even find a flange where the holes will line up!