Supporting on the hull bottom (right-side-up) is not advised.
I've been hauling my Outback on a Malone Gullwing, which cradles the hull of the yak. Am I asking for trouble? I can understand not placing the hull on flat crossbars, but since the Gullwing conforms somewhat to the shape of the hull, I figured it was OK. I don't see any deformation when it's strapped in.
I like the rack as it's very easy to load by myself, and none of my accessories (Scotty mounts, fishfinder bracket, etc.) get damaged by being dragged across the rails. Furthermore, since the straps and "wings" hug the yak very closely, I don't have to excessively tighten the straps, and there is very little strap exposed to the wind. (Nice and quiet.)