I would check with Reese, but my guess is the receiver extension will make the WD hitch ineffective. There will be enough flex/slop in the extension that I doubt you'll get much weight transfer to the receiver and truck frame.
Can the Sonata be towed with all 4 wheels on the ground? Or, what about a 2-wheel tow dolly to get the drive wheels off the road? Those might be better options than trying to pull a car on the trailer.
If you were to try using the WD hitch, then yes you'll need the camper and truck fully loaded before making any adjustments.
KJ
