if the wire dragged and ate through the rubber sheath, I would NOT attempt to repair, I would replace the whole pigtail (wire + 7 blade plug) to keep it weather tight and road worthy.
follow the cable into your trailer. somewhere, it goes into a junction box... disconnect the trailer battery
, AC, and solar
(if any) before working on this wiring. take lots of photos and/or draw a diagram before or while taking things apart, so you can put it together the same way.
if the pigtail cable disappears inside the trailer (not uncommon with fiberglass RVs), you might opt to cut it off about a foot from the trailer body, and get one of these pigtails with a integral junction box... slice open the foot long stub of factory cable, seperate out the wires, trim them to optimal lenghts, strip and crimp marine ring-terminals onto them, and secure them to this new external junction box, which you bolt to the inside of the trailer A-frame...