I am in the middle of a cross country trip so I thought I would share my car topping set-up. I am driving a Land Rover Freelander, which is the small Land Rover SUV. It is equipped with factory racks running fore and aft. I have fitted it with Thule Cross Roads and Load Bars. I originally ordered 50" Load Bars, but thankfully, Matt Crooks (CLC) sent 58" bars. The added length gives better room for tiedowns and they are above my head so no scalping problems. To the above I have added Malone Autoloader XVs on one side, just inboard of the cross roads. The bars, between the Malones and the farside cross roads are fitted with CLC cartopping pads. To all this I add my Shearwater 17 in the Malone racks and my MC 16.5, rightside up, on the pads. Each boat has two straps holding it to the carriers. Fore and aft each boat is tied to the bumper, being careful not to pull to hard and deform something. I also add a small line between the toggle carrers at each end so if one boat wants to pivot in its rack, the other provides resistance (my roof rack is pretty short and I have had the MC shift in a cross wind when not so thoroughly tied down). By the way, if you are pushed for interior space as we are, there is room between the boats to lash paddles to the Thule load bars.
The result: We have come 1300 miles (California desert to the Idaho mountains via Lake Tahoe) at highway speeds without a hitch. Unless I experience a headwind, I am comfortable at 65 mph. I use the cruise control so I don't sneek the speed up. As an additional note, I have interior bungie hold downs for my Shearwater hatches. For this trip I suplemented the hold downs with exterior bungies hooked to the perimeter lines. Still have my hatches. Hope this all is helpful to someone out there. I promise to confess if I do not still have two boats when I arrive home in early August.
Happy boat hauling!! Paul