While it was not easy, with the help of my son and the linked items from Amazon I was able to run a new cable from near the ceiling on one side to near the ceiling on the other side. Securely tape the new cable to the old, liberally lube it, and pull cable from where it is exposed under the RV.
Gardner Bender 79-006N Wire-Aide Wire Pulling Lubricant, Greaseless Fiber-Optic Wire Insulation, 1 Qt. Squeeze Bottle, Yellow
Gardner Bender EFT-15 Mini Cable Snake, 15 Ft Steel Fish Tape, Electrical Wire Fishing Tape, Red & Black https://www.amazon.com/dp/B074B3ZWMH/ref=cm_sw_r_fm_taa_hojrDb53JZPKA