You're talking about putting 1200+lbs of weight all behind the rear bumper of your 1500-series truck. That's really going to compress the rear suspension and have a major effect on the steering and handling of the truck to the point where it might actually be dangerous to drive, especially on wet roads.
A WD hitch could be used to spread the load out to the trailer and back to the front axle of the truck some, but I don't know of any receiver-mounted motorcycle carriers that can also double as WD-capable hitch extension. It would have to be custom.
Then, if the WD failed on the road you'd be sunk.
I know you don't like ramps up into the bed but really it's the only practical way of doing what you want to do.