When I needed to locate a leak in my old NT that the dealer failed to find, I found a trick that allowed me to get a pretty detailed look at the underside of my NT without to much work.
Using a camera and removing one or two screws to drop just enough of the corroplast to reach up and use the camera or your phone to take a series of either still or video pictures you can.
Taking photos of the side opposite of the rv. You can wiring runs the length of the rv.
There are now even cheap inspection cameras such as this one from harbor freight
https://www.harborfreight.com/digital-inspection-camera-61839.html
You can also find inspection cameras that can connect to your smartphone.
The inspection cameras may make it easier than even using a regular camera like I did to see the underside of the rv.