I used to live on a bumpy island, and invariably one strap would loosen a bit, so having four straps gave me piece of mind.
I also put the four cargo straps THROUGH the scupper holes in my tandem
, rather than simply over the top of the kayak. Two go through the front and two going through the back scupper holes (where the mirage drive goes on my tandem), and then through two holes/mounting points on the rails so there's no way the thing can slide and I don't
have to strap it so hard that I deform the kayak.
The kayak rests on the two aluminum crossbars I have attached to the rails, and I use a simple "swim noodle" under the crossbars to protect the roof because the bars do flex a bit. (non-flexing bars are on my budget list)
Loading from the back would be nice if my stupid brake light weren't right at the roofline. I used to worry about scuffing the bow on the ground when I raised the rear to the roof but after three years, it's no more scuffed than the rest of the boat.
I load the rudder/rear to the front of my Jeep because the scupper holes line up better with my rack/tie-downs. I have a tandem, so it might not matter with a single.
re: LIFTING the kayak to the roof...
I've been dreaming of a RAIL that slides out from my garage.
The rail has a sling pulley that raises the front of my kayak up to the vehicle roof line. And all I have to do is extend the rail to my Jeep, lift up the back of the kayak and slide it over the sling onto the roof. This would solve 1/2 of the loading problem, thus cutting the potential for an "old guy pulled back" by 50%.