Thanks you for the suggestion. I contacted Roadtrek and they were helpful.
They suggested I cut the panel in the bathroom to get at the wiring behind. I did that and was able to get to the broken link. I had to pull out the splice from behind the shower, but I was able to get to it completely.
Unwrapping the splice I found the problem right away. The scotch lock quick splice had worked itself out. My best guess is that being wedged between the chassis and the shower wall had done it over the 23 years, as well as heat and plastic depolymerization.
I stripped off some insulation from both wires, wedged the single-ended wire through the main, and soldered it up as a 'better' splice. Then taped it up and reassembled. The Roadtrek team suggested I add another panel to cover the cut. I may do that eventually, but for now it doesn't look too bad
This is just after removing the panel. I used a utility knife as suggested by Roadtrek. I was extremely nervous that there were other wires I would have cut, but the ones at the top were behind the insulation, and the offending taped splice at the bottom was behind where I ripped the panel off at the bottom.
Here's a picture of the scotch lock. You can see it's pretty mangled
Reassembled. I put a piece of tape behind the cut so that it would block the light from through the fiberglass