I didn't look at the Klenger's link. . but just run a "extension" into the bed and mount a 7 pin receptical there, have a extra foot or two of wire coiled under rig for later repairs mentioned later. .
7 pin male to original location route cable under bed up into box wall drill hole and mount 7 pin female connertor secured to bed wall. . that way you will have the 7 pin rear as needed... when not using the 5th wheel unplug the "extension" end and lay on top of the existing mount. . works great been doing it for a year now.
and easy repair when someone else helps ya and forgets to un plug the trailer and pulls out the receptical