Stan,

I do not have any experience with that particular rack, but I have car-topped my boats for many miles, including a 3000 mile treck last summer.  My MC 16.6 sits upright directly on the Thule load bars and my Shearwater 17 H sites on its side in Malone Auto Carriers attached to the load bars.  Both are strapped tightly to the carrier and gently secured fore and aft.  I have not seen a boat that was not ridgid enough to withshant the loads from the straps holding it to the carrier.  The daner comes with bow and stern lines.  Most racks are pretty short fore and aft, compared with the boat.  So, it is very important to secure the boat at the bow and stern to keep it from swinging sideways at 70 MPH.  These lines must be tensioned delecately.  They want to be snug to keep the boat in place, but not so tight that they bend it.  The car may flex a bit as you zoom thru those dips in the road and that is going to put some additional loads on the boat.  I used to carry my MC 16.5 right side up on the factory racks of a Ford Expedition with the bow and stern lines quite tight.  At some point in its journeys it definitely got overstressed, resulting iin a deck crack at the aft corner of the cockpit, so it can happen.

Best bet:  snug the boat into your roof racks and gently tension bow and stern lines.  Keep an eye on the position of the bow as you drive and ceck it all for security often.  Good luck and enjoy the road.

Paul