On my 5th wheel the generator will charge the batteries on the 5th wheel through the converter/charger and 12V is sent to the truck through the pigtail plugged into the truck. No damaging feedback since the 12V system is isolated from the 110V system in the 5th wheel.
What you are proposing will work. But you'll need to make sure your power cord is securely attached from the truck to the 5th wheel with slack to allow for turns. I saw a guy towing down the road with his power cord dragging on the ground. It had come loose on a bumpy section of road. Luckily he stopped when I flagged him down befor there was too much damage.