I think you are over thinking this. The JS is a little boat.  The trailer will be small too.  Properly bunked you should need a strap across the stern, and a  bow tie down to the winch.  If you have a winch. The typical strap for that would have a hook on both ends and a cam-lock device, that adjusts length,  in the middle.  The strap would normally be a 2 - 3" wide strap.  Not the 1" wide straps of the kayaks. 

I would recommend removing the motor before trailering far. When on the boat a safety line to the motor is always a good idea.  I don't recommend muscling the boat on and off the trailer. Floating is easier, but if you are young and able go ahead.  Putting a tape measure across the boat sitting on the trailer is often the way I determine length. Then cut a long strap to fit. (melt the end)

On mine I had to built bunks that fit between the center console boat bunks and tie that down. Then the boat sits on the bunks and gets strapped down.  Of course that's to take it a short distance on a big trailer when the big boat is somewhere else.   I use an old jet ski hoist to put it in and out of the water normally. The trailer transport is for storm garaging.  

Kayaks and canoe straps.............. these boats often get transported on horizontal bars fited across the trailer/car/truck from side to side.  The straps go over the boat, drop down to  the bar, loop underneath, return over the top, drop down under the bar if front of you and make a connection in front of you.  Thus they are likely "double strung".  Canoe straps would be longer on say a 17ft canoe than a 17ft kayak.  Canoes are generally "fatter".