adding second shore power receptacle

Far from an electrical genius, but wouldn't the OP just need a fused or enclosed manual knife switch type disconnect to isolate the existing shore connection from it's power center connection in the RV when he's running the generator? A transfer switch would be appropriate if the generator was permanently installed/wired in the trailer. That said, I would think relocating the shore connection (though probably aggravating and time consuming) to/toward the front of the trailer would be the safer option, no worries about back feeding power.