The best solution I have found is to run a piece to 3/6" plate on top on the bed rail in the horizontal position. you make it stick out far enough that it is where the upright piece of the rack attaches. This method allows you to build the rack as an exoskeleton. As far as loading, I weld two sets of brackets on the rear cross bar to attach two 24" rollers. The roller can be found at material handling suppliers.
To load you have two people on the front handles lift the nose up and sit it against the the rack or topper. Then continue to work the boat in to the most vertical position you can get it. Then everyone moves the the back and lifts the stern, but keeps it low to achieve a large angle of attack and maximize the effect of the roller. Then finally 1.2.3. push and she lands in the middle of the rack.
It will realistically take at least 3 people to load and 2 to unload. If you want to talk about designs or anything else contact me through my business. [email protected]
If you want to come down for a rogue trip in southern Oregon I could do the build while you were on the river.