I am wondering if anyone has experience with a "car-top" rig for use with a convertible? I have a recent vintage Saab convertible and a Mill Creek 16.5. I can invisage a tee bar that fits into a square socket hitch on front and back. The kayak would obviously be supported only by the two tees, along with the bow and stern lines, but the MC's flat bottom might just accomodate such a rig.
Don't know whether the underbody of the Saab could accept the mountings, and I don't know that the aerodynamics would be acceptable. Obvisously I'd want to be able to remove the tee bars when not in use.