I have a PA14 and a Toyota Highlander. Here's my load/carry rig. I made up a guide and support board to keep the bow from sliding sideways off the car's spoiler. Then there are a pair of Hully rollers bolted to the rear Thule bar. They guide and support the keel as I push the boat up.
On the front bar, I made up a wooden block to fit inside the drive well. I simply slide the boat forward and lower it onto this block. Once there, the boat can't shift in any direction.
I use two ratcheting straps that run inside the handle rails and under both the car rails and the Thule bars, plus two tiedowns to the front bumper. My Prangler isn't going anywhere unless I roll the whole rig.