This will help. I wanted to protect the rear spoiler on my Toyota Highlander, as well as keep my ProAngler 14 from sliding sideways in uneven parking situations. I glued and screwed two pieces of 2x2 to an old cutting board, then bent two pieces of steel strapping to hook around my rear crossbar. I set the bow of my Prangler between the two guides, then go around and lift the stern. The two Hully Rollers then guide and ease the boat forward.
I also made a safety block of wood and bolted it to the front crossbar (visible between the Rollers above). The drive hole fits right over this block to keep the boat from shifting forward/aft or side/side. View from the side:
Two ratcheting straps and two front tiedowns make the rig as safe and secure as possible.