As others have shown, car topping a PA can look and sound very intimidating but it really isn't all that bad at all. You never lift more than half of the kayak at a time. I believe the height and angle can play more of a factor than the weight.
On my Jeep Wrangler I use the Thule Hydro-Glide saddles on the rear and the Set-To-Go saddles on the front. I have the rear of the PA lined up with the racks and the nose up to beside the rear tire. I lift the front up to the rack then walk back and lift the rear and slide forward. It slides very easy on the Hydro-Glides. Coming down is just the reverse.