Elec. cable scuffing tailgate. Help

Well I had the plug in the bed of my 07 Chevy but many holes were drilled and the RV shop that installed it had to use inline splices with elec. tape. Saw many problems down the road with rust and wire corrosion. Decided to go a new route with the new truck and not drill through factory spray in bed liner. This is a short bed truck and Toyota does not allow the 5th. Wheel wiring option. My hitch is mounted ahead of rear axel so with the side winder all of the kingpin is inside of the tailgate. The only place to "hang" something would be on the underside of the trailer. Don't really want to drill there either.